KEYWORDS: X-rays, Tomography, Signal to noise ratio, Scanning electron microscopy, Electron beams, Nanowires, X-ray imaging, Sensors, X-ray detectors, Spatial resolution
We aim at resolving deca-nanometer features in microelectronic samples using a laboratory SEM-based X-ray tomography
microscope. Such a system produces X-rays through the interaction between a focused SEM electron beam and a metallic
target. The effective source size of the X-ray beam can be adjusted by varying the target material and geometry. For
instance, the use of tungsten nanowires (few hundred nanometers of length) combined with a high electron beam current
leads to an increased X-ray flux generated in a reduced volume, necessary for detecting interface details of the analyzed
object. It improves resolution and signal-to-noise ratio (SNR), but is also sensitive to electron beam-target instabilities
during the scan. To improve robustness, a FFT-based image correlation is integrated in the process through a closed-loop
control scheme. It allows stabilizing the electron beam on the target and to preserve the X-ray flux intensity and alignment.
Also, a state of the art high-resolution scientific-CMOS (sCMOS) X-ray detector was installed, allowing to reduce noise
and to increase quantum efficiency. Results show that such numerical and equipment improvements lead to significant
gains in spatial resolution, SNR and scanning time of the SEM-based tomography. It paves the way to routine, high
resolution, 3D X-ray imaging in the laboratory.
A novel soft X-ray source has been developed that generates soft X-rays of 2.36 nm wavelength. The source is based on focusing a 10 keV electron beam on a continuous jet of water, exciting oxygen K(alpha ) characteristic radiation. A high-resolution spectrum was recorded which shows a background-free peak at 2.36 nm with a FWHM of 0.017 nm. The brightness of this source is limited by the amount of electron energy that can be dissipated inside the water jet, without endangering the stability of the source. We succeeded in focusing 60 (mu) A onto one side of the jet, at which value the brightness is ~5*108 photons/(sec sr micrometers 2). The source is of potential interest for use in tabletop soft X-ray microscopy, because the line radiation falls just within the water window, the wavelength region that is employed in this type of microscopy.
Starting from different fine structure levels in the metastable c3IIu- triplet state of molecular hydrogen, we excite ro-vibrational levels in the n equals 3 triplet gerade complex. The linear polarization of the laser results in an alignment of the molecular plane with the polarization vector. This is then reflected in an anisotropy of the photofragments. We show that the anisotropy parameters are influenced by the presence of the electron spin, which causes the fine structure splitting. We compare our results to theoretical expressions for the anisotropy parameter which incorporates the fine structure of the initial and final states.
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