LamNI – an instrument for X-ray scanning microscopy in laminography geometry

Abstract

Across all branches of science, medicine and engineering, high-resolution microscopy is required to understand functionality. Although optical methods have been developed to `defeat' the diffraction limit and produce 3D images, and electrons have proven ever more useful in creating pictures of small objects or thin sections, so far there is no substitute for X-ray microscopy in providing multiscale 3D images of objects with a single instrument and minimal labeling and preparation. A powerful technique proven to continuously access length scales from 10 nm to 10 µm is ptychographic X-ray computed tomography, which, on account of the orthogonality of the tomographic rotation axis to the illuminating beam, still has the limitation of necessitating pillar-shaped samples of small (ca 10 µm) diameter. Large-area planar samples are common in science and engineering, and it is therefore highly desirable to create an X-ray microscope that can examine such samples without the extraction of pillars. Computed laminography, where the axis of rotation is not perpendicular to the illumination direction, solves this problem. This entailed the development of a new instrument, LamNI, dedicated to high-resolution 3D scanning X-ray microscopy via hard X-ray ptychographic laminography. Scanning precision is achieved by a dedicated interferometry scheme and the instrument covers a scan range of 12 mm × 12 mm with a position stability of 2 nm and positioning errors below 5 nm. A new feature of LamNI is a pair of counter-rotating stages carrying the sample and interferometric mirrors, respectively.

First ptychographic X-ray computed tomography experiment on the NanoMAX beamline

“…As the beam is focused by a KB mirror system, the photon energy could be changed rather easily and by only slightly changing the beam footprint on the sample [see Bjö rling et al (2020)], but not shifting the focus position along the beam axis, allowing for resonant experiments around absorption edges for additional chemical contrast (Donnelly et al, 2015). Using the goniometer below the base stages, the angle between the rotation axis of the sample and the X-ray beam could be changed, allowing for possible laminography experiments on extended samples (Holler et al, 2019(Holler et al, , 2020. For all of the mentioned methods it is possible to use physical centring to the rotation axis using manual centring stages, or virtual centring using the base motors, as in the experiment presented here.…”

“…As of now, the position of the sample is only measured by the encoders of the piezo-scanning stage. Additional independent sample tracking via interferometers as utilized in similar setups (Schroer et al, 2017;Holler et al, 2018Holler et al, , 2020Deng et al, 2019;Tolentino et al, 2019) is desirable, as positional errors are more difficult to handle with measurements using a small probing beam, due to the smaller absolute overlap between neighbouring positions. Interferometers would also allow direct measurement of the required relative positions between the (housing of the) optics and the sample, with high accuracy and separate from any encoder measurements.…”

State-of-the-Art High-Resolution 3D X-ray Microscopy for Imaging of Integrated Circuits

“…[28] In contrast to tomography, where the axis of rotation is perpendicular to the x-ray propagation direction, the angle between the rotation axis and the beam propagation is smaller in the case of laminography. In the setup of a dedicated microscope called laminographic nano imaging (LamNI), [29] this laminography angle is 61 degrees. Figure 4a shows the PyXL geometry and Fig.…”

“…Laser interferometry measures the relative position of the sample with respect to the lens, similar to the tomography setup, and enables accurate sample positioning. Further details can be found in Holler et al [29] To demonstrate the imaging of ICs via PyXL a chip with general purpose logic manufactured in 16 nm FinFET technology was selected. The only sample preparation required was a mechanical polishing of the silicon substrate to a thickness of 20 µm to achieve su icient x-ray transmission at the 6.2 keV photon energy used.…”

Alignment methods for nanotomography with deep subpixel accuracy

“…Details of the measurement, acquired at the cSAXS beamline, Paul Scherrer Institut (PSI), Switzerland, can be found in [55]. The measurements were acquired in the laminography nano-imaging instrument (LamNI) [56] equipped with optimized illumination optics [57]. The sample was an integrated circuit (IC) printed using 16 nm node technology.…”