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edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 2 14 reached a resolution of approximately 150 nm, [14] limited by the scanning stability and accuracy, and is comparable to lens-based systems. A project to develop dedicated instrumentation fol- lowed at PSI shortly after. The instrumental difficulty is to achieve accurate sample scanning with a precision better than the target resolution, while also allowing a full 180- degree rotationof the sample for tomography. Key to these state-of-the-art instruments is dedicated and patented laser interferometry that measures the relative position of the x-ray beamand the sample, [15] whichminimizes the interferometry deadpath and is compatible with rotation via a hemispherical reflective reference mirror and track- ing interferometer. Figure2 shows a schematicof an instru- ment called a flexible tomography nano imaging (flOMNI) endstation. [16,17] The x-ray beamenters an optics unit with a collimating lens optics (central stop (CS), Fresnel zone plate (FZP), order sorting aperture (OSA)) and propagates to the sample which is installed on a reference mirror. Differential interferometry then measures the relative position between the beam defining x-ray collimator and sample in the plane perpendicular to the x-ray beam propagation direction. The reference mirror is installed on a combination of piezo stage and rotation stage. The x-ray diffraction patterns are recorded by a detector in the far-field. This position metrology, in closed-loop control, allows accurate samplepositioning, whichenables record- ing distortion-free high-resolution projections. With dedi- cated algorithms, [4,9,18,19] the ptychographic projections are reconstructed and aligned, to be subsequently combined to recover the 3D object. [20,21] To demonstrate the imaging of an integrated circuit, a cylindrically shaped sample was prepared and extracted from the ASIC, againmade with 110 nmnode technology, Fig. 1 (a) Experimental setup for recording x-ray ptychography data in 2D with an example of a recorded diffraction pattern. (b) Reconstructed object (phase) recorded in an ASIC (110 nm node). (c) Zoom of the region marked with the red square in (b) with an overlay of the chip design. (d) Layered structure of the ASIC. Image adapted from Guizar-Sicairos et al. [10] with permission from the Optical Society. Fig. 2 Schematic of the flOMNI instrument which enables ptychographic tomography measurements. Posi- tioning accuracy is achieved via dedicated laser interferometry and closed-loop control. Image repli- cated from Holler et al. [17] using a focused ion beam. The 10 µm diameter sample was mounted on a tomography pin [22] to be accessible by the x-rays from the full span of 180 degree sample rota- tion. 600 projections equally spaced in angles using x-ray ptychography were acquired and reassembled using 3D volume reconstruction. Corresponding 3D renderings generated by threshold segmentation and labeling are depicted in Fig. 3, showing the layered structure, with a capacitive element, vias, and the transistors in the lower region. Surface artifacts from the manufacturing process are clearly visible. Figure 3b shows a view of the tran- sistor region, where it becomes apparent that the gate contacts are varying in thickness and appear not to be fully connected. In addition to imaging a known circuitry, unknown samples were also imaged. An Intel processor, this time (a) (b) (c) (d)