Journal of X-Ray Science and Technology - Volume 4, issue 3
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Journal of X-Ray Science and Technology is an international journal designed for the diverse community (biomedical, industrial and academic) of users and developers of novel x-ray imaging techniques. The purpose of the journal is to provide clear and full coverage of new developments and applications in the field.
Areas such as x-ray microlithography, x-ray astronomy and medical x-ray imaging as well as new technologies arising from fields traditionally considered unrelated to x rays (semiconductor processing, accelerator technology, ionizing and non-ionizing medical diagnostic and therapeutic modalities, etc.) present opportunities for research that can meet new challenges as they arise.
Abstract: Soft x-ray projection lithography (SXPL) is an attractive technique for the fabrication of high-speed, high-density integrated circuits. In an SXPL stepper, the x-ray imaging mirrors consist of multilayer coatings deposited onto high precision substrates. The stepper is intended to fabricate ultra-high spatial-resolution structures with a minimum feature size of <0.1 μm. To achieve this resolution, the imaging mirrors must maintain a very precise surface figure while being exposed to x radiation. Failure to achieve and maintain the mirror surface figure will distort the wavefront propagating through the imaging system and will degrade system resolution. The required surface figure accuracy for…each imaging mirror depends upon the required resolution, the wavelength, and the optical design. For conventional SXPL stepper designs, the total (peak-to-valley) surface figure error budget per mirror is approximately ±1 nm. Due to material properties at soft x-ray wavelengths and practical fabrication considerations, x-ray multilayer mirrors have limited reflectivities. A fraction of the incident x radiation is absorbed in the multilayer coating. This absorbed radiation constitutes a thermal load on the mirror, thereby distorting its shape and compromising the accuracy of its surface figure. In this paper, we analyze the thermally induced distortion on the imaging optics and conclude that the maximum allowable thermal distortion limits the maximum allowable x-ray power transported to the wafer and limits the minimum acceptable multilayer mirror reflectivity. The penalty for either insensitive x-ray resists or inefficient mirror reflectivity is a decrease in system throughput which cannot be compensated with increased source power either collected by condenser optics or generated by the source.
Abstract: In order to fabricate entrance windows for soft x-ray detectors, various technologies have been developed. Depending on the x-ray-detector type and the environment in which the windows are used, entrance windows must meet several, often contradictory, requirements: while good pressure tolerance and durability as well as gas tightness require thicker structures, good x-ray transmission can only be achieved with thin membranes. In this paper, the suitability of different window types for various applications is discussed. The applicability discussion is based on the results of tests performed on prototype windows, as well as on calculated and measured x-ray transmission properties. A…comparative study of endurance vs transmission properties of some candidate membrane materials is also presented. Test results include pressure tolerance and leakage rates as well as some measurements of radiation damage to the window materials. The window technologies presented include coated polyimide membranes with two different supporting schemes as well as submicrometer beryllium membranes.
Abstract: Measured values for image noise variance in x-ray computed tomography were found to be less than half of the values predicted by published formulas. This phenomenon had previously been attributed qualitatively to the use of linear interpolation of the filtered projections in the back projection process. An analysis of the reconstruction process has allowed the derivation of a formula for image noise variance which incorporates the effect of this interpolation, giving results which are less than 50% of the previously predicted values. This formula has been tested with images of a perspex rod produced by an x-ray microtomography scanner and…with a similar image derived from mathematically modeled projection data. The predicted noise variance was within 1% of the measured values for both the simulated and the experimental data.
Abstract: Grazing x-ray reflectometry allows analysis of thin-layer stacks. The fitting of the reflectivity curve by a trial and error method can determine the parameters of the films. The Fourier analysis of the experimental reflectivity curve can directly give a rough determination of the profile index. Such results can be useful in choosing a starting model. With the choice of an appropriate model a fit to the reflectivity curve can be undertaken to determine the parameters of the stack. The Fourier analysis method can only be used if the reflectivity data undergo a transformation to produce a periodic curve. Associated artifacts…are studied and discussed. Each Fourier peak is associated with two interfaces. The interface roughness spreads the Fourier peaks, adding the squared roughness values. The sample’s absorption of the x-rays does not limit the Fourier analysis.
Abstract: A method is proposed for measuring different energy ranges of x-ray radiation with the same spectrometer crystal employing structural phase transitions. When the crystal temperature is varied beyond the phase transition temperature, the crystal symmetry is altered predictably and reversibly. Thus, with no change in the angle of glancing incidence, the x-ray beam hits in different crystal phases different lattice planes which correspond to different energy ranges. The advantage is that neither large motions nor exchanging the spectrometer crystal is necessary during observations.
Abstract: The characterization of a Si(Li) detector used for PIXE analysis is presented. The main detector parameters are indicated, and the different methods of determining them are examined. Also, the detection efficiency has been measured in the 1.4-100 keV photon energy range, using calibrated radioactive sources and PIXE, to obtain and compare the fitted parameters. Finally, the fit of an analytic function to the measured efficiency values and the efficiency in parametric form are compared, and the advantages observed for each are noted.