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Influences on 3D image quality in a high-resolution Xray laminography system

: Ebensperger, Thomas; Rimbach, Charlotte; Zabler, Simon; Hanke, Randolf

Postprint (8.8 MByte; PDF; )

Journal of Instrumentation 9 (2014), No.5, Art. C05030, 10 pp.
ISSN: 1748-0221
International Workshop on Radiation Imaging Detectors (IWORID) <15, 2013, Paris>
Journal Article, Conference Paper, Electronic Publication
Fraunhofer IIS ()
Fraunhofer IZFP ()
X-ray generators; inspection with x-rays; X-ray sources

Recently, we demonstrated that projective X-ray microscopy is feasible with a twodimensional spatial resolution down to 100 nm by using laboratory nanofocus X-ray sources and a geometric magnification of up to 1000x. Based on these previous results, we developed a high-resolution X-ray laminography system which uses an optimized thin-film X-ray transmission target together with a modified electron probe micro analyzer. Unlike conventional axial computed tomography (CT), 3D laminography imaging involves a linear translation of both detector and object with respect to a stationary point source. In this contribution we present a detailed characterization of the setup concerning especially the laminographic imaging mode. The quality of the volume reconstruction is assessed by simulating an ideal setup with an analytical model including features down to 200 nm which are resolved in the setup given a high enough SNR in the projections. We further address the issue of a drop in the detector resolution under oblique X-ray illumination which is a common problem to such systems. The finite penetration depth of the X-rays into the detector pixels causes an anisotropic blurring of the detector point spread function (PSF) under oblique irradiation. We tested the influence of this blurring by calculating the illuminationdependent modulation transfer function (MTF) of the detector. Our measurements are supported by numerical simulations of the detector MTF. Both simulations and measurements show a drop in spatial resolution (20% of the MTF) from 12.5 lp/mm (irradiation perpendicular to the detector screen) down to 5.2 lp/mm (irradiation 30 degrees oblique to the screen). Furthermore, first examples of 3D imaging of test structures and material imaging are given.