The recent proliferation of artificial intelligence and machine learning applications relying on large language models is fueling unprecedented demand for compute capacity. Associated with this is a need to scale capacities of short-reach optical transceivers towards multiplex Terabit/s, while maintaining integration density (frontpanel or beachfront density) and energy efficiency (pJ/bit). One option to scale transceiver capacity is to increase the bandwidth per lane from today's 200G to 400G or even higher: coherent transceiver technology is then expected to play an ever more important role. Photonics and electronics with higher bandwidths beyond 100GHz will play a crucial role. Integration of thin-film LiNbO3 modulator onto a Silicon Photonics platform is shown to be a viable option to meet the needs for new generations of optical transceivers. Front-end electronics such as linear modulator drivers and transimpedance amplifiers can rely on traveling-wave design approaches to allow continued bandwidth scaling despite (relative) slowing transistor speeds. Novel wireline data converter architectures can be used to overcome limitations of existing implementations. Maintaining signal integrity from photonics and electronics can be facilitated using both 2.5D and 3D integration approaches. While the introduction of novel materials and architectures will require time to further mature, optical transceivers operating at baudrates up to and beyond 200Gbaud are now just beyond the horizon.

Atom probe tomography (APT) is a unique analytical technique that offers three-dimensional elemental mapping with a spatial resolution down to the sub-nanometer. When APT is applied on complex heterogenous systems and/or under certain experimental conditions, that is, laser illumination, the specimen shape can deviate from an ideal hemisphere. Insufficient consideration of this aspect can introduce artifacts in the reconstructed dataset, ultimately degrading its spatial accuracy. So far, there has been limited investigation into the detailed evolution of emitter shape and its impact on the field-of-view (FOV). In this study, we numerically and experimentally investigated the FOV for asymmetric emitters and its evolution throughout the analysis depth. Our analysis revealed that, for asymmetric emitters, the ions evaporated from the topmost region of the specimen (summit) project approximately to the detector center. Furthermore, we demonstrated the implications of this finding on the FOV location for asymmetric emitters. Based on our findings, the location of the center of the FOV can deviate from the specimen central axis with an evolution depending on the evolution of the emitter shape. This study highlights the importance of accounting for the specimen shape when developing advanced data reconstruction schemes to enhance spatial resolution and accuracy.

OrbiSIMS is a secondary ion mass spectrometry method with dual mass analyzers: a time-of-flight (ToF) mass spectrometer for high-speed imaging and an Orbitrap™ for high mass resolving power and mass accuracy. Originally developed for biological imaging, there is now growing interest in the application to semiconductor materials to resolve peak interferences that obfuscate analysis in traditional SIMS depth profiling experiments. We use a new method to calibrate the Orbitrap intensity scale to true counts, which allows comparison of the useful yield and duty cycle with a magnetic sector instrument and a time-of-flight instrument using an Sb implant in the silicon sample. The useful yield of the Orbitrap and magnetic sector instruments (for one detected peak) are similar. However, since the magnetic sector instrument has serial mass detection, its useful yield reduces as more peaks are analyzed. While the ToF instrument has parallel detection, it has a low duty cycle and the useful yield is two orders of magnitude lower for 1000 eV Cs+ sputtering. The depth resolution was also compared from the measurement of the downslope from depth profiles of an Sb delta multilayer. For 1000 eV Cs+ sputtering, the downslopes are 3.9, 2.3, and 2.7 nm/decade for Orbitrap, magnetic sector, and ToF instruments, respectively. Ion trajectory simulation shows that the poorer depth resolution of the OrbiSIMS is in part due to ion beam distortion at low energy.

We realize the quantitative determination of the spatial dimensions of nanopatterns using Rutherford backscattering spectrometry (RBS) with a mm-sized ion beam. The methodology is based on the effects of the nanopatterns on the RBS signal from the substrate. We demonstrate the approach with the study of a periodic pattern of 35 nm wide and 75 nm high SiO2 lines which have a periodicity of 90 nm. We analyse the relation between the features in the experimental spectra and the properties of the nanostructures. Current voxel-based simulation software allows to reproduce many of the experimental observations well. However, we found that the present simulation software inadequately incorporates the effect of the angular spread due to the finite detector size. We propose a method to model the effect more accurately and through this we demonstrate a dramatically improved agreement with the experimental spectra.

The demand for compute capacity is currently doubling every 3.4months. This has accelerated the need for Terabit optical transceivers for data centre applications. Scaling options, and photonic and electronic technologies that can meet such demand are presented.

Rutherford backscattering spectrometry (RBS) is an analytical method able to provide quantitatively elemental information with high accuracy in the near surface region of samples. However, the technique conventionally lacks the required (sub)micron spatial resolution for many semiconductor applications. Firstly, the ion beam current of a highly focused beam is very small, limiting the analytical sensitivity of the measurement. Secondly, the exposure of a sample to a highly focused ion beam readily leads to sample damage, surface sputtering, and accordingly to a measurement error. As a solution to these problems, ensemble RBS is presented whereby multiple devices are measured simultaneously using a broad beam. A judicious choice of the scattering conditions and related data interpretation nevertheless leads to the ability to analyse 3D-devices of micrometre sizes. We demonstrate the potential of this approach through the analysis of atomic species present on the different surfaces of 3D-microfluidic devices. The performance of the technique is demonstrated by the analysis of microfluidic devices after Pt deposition at an oblique angle, and the analysis of the same microfluidic devices after a site-selective deposition of a sub-monolayer of Hf. Further, the performance of ensemble RBS on these structures is compared to the one of microbeam RBS.

We present a site-specific elemental analysis of nano-scale patterns whereby the data acquisition is based on Rutherford backscattering spectrometry (RBS). The analysis builds on probing a large ensemble of identical nanostructures. This ensures that a very good limit of detection can be achieved. In addition, the analysis exploits the energy loss effects of the backscattered ions within the nanostructures to distinguish signals coming from different locations of the nanostructures. The spectrum deconvolution is based on ion-trajectory calculations. With this approach, we analyse the Ru area-selective deposition on SiO 2 -TiN line-space patterns with a linewidth of 35 nm and a pitch of 90 nm. We quantify the selectivity and the Ru local areal density on the top versus on the sidewall of the SiO 2 lines. The sensitivity to probe ruthenium deposited on the various surfaces is as low as 10 13 atoms/cm 2 . The analysis is quantitative, traceable, and highly accurate thanks to the intrinsic capabilities of RBS.

Shrinking semiconductor device dimensions requires extensive R&D in all areas, inclusive of the materials characterization techniques and methodologies commonly used. With dimensions now being much smaller than the beam spot sizes of usual characterization methods like SIMS, RBS, etc., new concepts are needed. In this context, the application of Self-Focusing SIMS (SF-SIMS) to determine the bulk composition of structures of exceedingly small dimensions was demonstrated in the past years. However, due to the extensive use of secondary ions of higher m/z in the SF-SIMS concept, high mass resolution is often required; this is to avoid possible mass interferences that limit the SF-SIMS method to reach low detection limits and/or to unambiguously identify the ion signals. Although the mass resolving power of Time-of-Flight (ToF) analyzers of SIMS instruments is considered high (m/Delta m -10000), it still presents a restriction for the SF-SIMS methodology on specific systems. The OrbitrapTM mass analyzer allows an increase in the mass resolution up -20x along with mass accuracy levels below one ppm. In this study, we demonstrate that the mass resolving power of the OrbitrapTM-SIMS allows to resolve limiting mass interferences, thereby allowing accurate quantification of impurities/dopants in small finFET structures (<20 nm).

For atom probe tomography, multihits and any associated ion pile-up are viewed as an "Achilles" heel when trying to establish accurate stoichiometric quantification. A significant reason for multihits and ion pile-up is credited to co-evaporation events. The impact is the underestimation of one or more elements present due to detector inadequacies when the field evaporated ions are spatially and temporally close. Nitride materials, especially GaN and AlN, have been shown to suffer a strong field dependent compositional bias, with N having the characteristics for being a species prone to ion pile-up. In this paper we have explored through field dependent measurements on GaN and AlN the associated impact of co-evaporated multihits and ion pile-up. To achieve this a normal CAMECA electrode along with a specially modified GRID electrode, which was designed to manipulate co-evaporated ions and hence ion pile-up, were employed. From our results and in-depth analysis, any co-evaporation and associated ion pile-up is found to be either very small, or not species dependent. Thus, ion pile-up cannot be attributed as the cause for the significant N underestimation observed in these materials.

Raman spectroscopy is an effective tool for stress and compositional metrology in the semiconductor industry. However, its application toward decoupling a complex stress state in semiconductor materials requires the use of liquid immersion lenses that are process line incompatible. In this work, a practical design concept for off-axis Raman spectroscopy is presented. By tilting the incident light away from the normal incident axis, forbidden Raman modes can be accessed allowing determination of the in-plane stress tensor in semiconductor materials. Furthermore, we benchmark off-axis Raman spectroscopy against oil-immersion Raman spectroscopy for stress characterization in 20 nm-wide strained Ge fin field-effect transistor channels. We demonstrate that off-axis Raman allows anisotropic stress metrology without reliance on liquid immersion lenses, highlighting its viability in the process line. The stress state is validated through nanobeam diffraction measurements.

A major challenge for atom probe tomography (APT) quantification is the inability to decouple ions that possess the same mass–charge (m/n) ratio but a different mass. For example, 75As+ and 75As22+ at ∼75 Da or 14N+ and 28Si2+ at ∼14 Da cannot be differentiated without the additional knowledge of their kinetic energy or a significant improvement of the mass resolving power. Such mass peak overlaps lead to ambiguities in peak assignment, resulting in compositional uncertainty and an incorrect labeling of the atoms in a reconstructed volume. In the absence of a practical technology for measuring the kinetic energy of the field-evaporated ions, we propose and then explore the applicability of a post-experimental analytical approach to resolve this problem based on the fundamental process that governs the production of multiply charged molecular ions/clusters in APT, i.e., post-field ionization (PFI). The ability to predict the PFI behavior of molecular ions as a function of operating conditions could offer the first step toward resolving peak overlap and minimizing compositional uncertainty. We explore this possibility by comparing the field dependence of the charge-state-ratio for Si clusters (Si2, Si3, and Si4) with theoretical predictions using the widely accepted Kingham PFI theory. We then discuss the model parameters that may affect the quality of the fit and the possible ways in which the PFI of molecular ions in APT can be better understood. Finally, we test the transferability of the proposed approach to different material systems and outline ways forward for achieving more reliable results.

Reliable spatially resolved compositional analysis through atom probe tomography requires an accurate placement of the detected ions within the three-dimensional reconstruction. Unfortunately, for heterogeneous systems, traditional reconstruction protocols are prone to position some ions incorrectly. This stems from the use of simplified projection laws which treat the emitter apex as a spherical cap, although the actual shape may be far more complex. For instance, sampled materials with compositional heterogeneities are known to develop local variations in curvature across the emitter due to their material phase specific evaporation fields. This work provides three pivotal precursors to improve the spatial accuracy of the reconstructed volume in such cases. First, we show scanning probe microscopy enables the determination of the local curvature of heterogeneous emitters, thus providing the essential information for a more advanced reconstruction considering the actual shape. Second, we demonstrate the cyclability between scanning probe characterization and atom probe analysis. This is a key ingredient of more advanced reconstruction protocols whereby the characterization of the emitter topography is executed at multiple stages of the atom probe analysis. Third, we show advances in the development of an electrostatically driven reconstruction protocol which are expected to enable reconstruction based on experimental tip shapes.

This paper describes a reconstruction method for atom probe tomography based on a bottom-up approach accounting for (i) the final tip morphology (which is frequently induced by inhomogeneous evaporation probabilities across the tip surface due to laser absorption, heat diffusion effects, and inhomogeneous material properties), (ii) the limited (and changing) field of view, and (iii) the detector efficiency. The reconstruction starts from the final tip morphology and reverses the evaporation sequence through the pseudo-deposition of defined small reconstruction volumes, which are then stacked together to create the full three-dimensional (3D) tip. The subdivision in small reconstruction volumes allows the scheme to account for the changing tip shape and field of view as evaporation proceeds. Atoms within the same small reconstruction volume are reconstructed at once by placing atoms back onto their possible lattice sites through a trajectory-matching process involving simulated and experimental hit maps. As the ejected ion trajectories are simulated using detailed electrostatic modeling inside the chamber, no simplifications have been imposed on the shape of the trajectories, projection laws, or tip surface. We demonstrate the superior performance of our approach over the conventional reconstruction method (Bas) for an asymmetrical tip shape.

First-principles calculations are used to systematically investigate the impact of surface effects on the energetic cost to incorporate point defects near the growing surface [Ge(001)] and its consequence on the dopant activation in P-doped Ge layers. We illustrate the formation enthalpy ΔHf for the incorporation of a mono-vacancy, which is the dominant point defect responsible for the electrically inactive dopant incorporation in P-doped Ge. The calculated values point toward a significant lowering of ΔHf near the growing surface in comparison to the bulk cubic Ge supercell. The impact of the surface almost vanishes beyond the sixth atomic monolayer located below the surface and the calculated ΔHf values overlap with the ones computed for a bulk cubic Ge supercell. For epitaxial Ge:P layers, grown at low growth temperatures (<450°C) using the deposition method such as the Chemical Vapor Deposition, the dopant-vacancy clusters are formed within the first few monolayers close to the growing surface. The low ΔHf values for the incorporation of a mono-vacancy near the growing surface suggest that the concentration of vacancies can be significantly enhanced with respect to the bulk Ge, which can subsequently trap more dopants and deactivate them at the surface itself. Our first-principles calculation results are in line with previously reported experimental positron annihilation spectroscopy analysis on Ge:P layers grown at 440 °C using GeH4 as gas precursor. At P concentrations above 1×1020cm−3, the mono-vacancy sized open-volume defects are passivated by at least three P atoms.

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Strain engineering in semiconductor transistor devices has become vital in the semiconductor industry due to the ever-increasing need for performance enhancement at the nanoscale. Raman spectroscopy is a non-invasive measurement technique with high sensitivity to mechanical stress that does not require any special sample preparation procedures in comparison to characterization involving transmission electron microscopy (TEM), making it suitable for inline strain measurement in the semiconductor industry. Indeed, at present, strain measurements using Raman spectroscopy are already routinely carried out in semiconductor devices as it is cost effective, fast and non-destructive. In this paper we explore the usage of linearized radially polarized light as an excitation source, which does provide significantly enhanced accuracy and precision as compared to linearly polarized light for this application. Numerical simulations are done to quantitatively evaluate the electric field intensities that contribute to this enhanced sensitivity. We benchmark the experimental results against TEM diffraction-based techniques like nano-beam diffraction and Bessel diffraction. Differences between both approaches are assigned to strain relaxation due to sample thinning required in TEM setups, demonstrating the benefit of Raman for nondestructive inline testing.

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Atom probe tomography, thanks to the advent of laser-assistance (LA-APT), is becoming a promising tool for confined volume materials characterization in the semiconductor industry. A prime example is APT’s potential for dopant profiling, or more general compositional analysis, in confined three dimensional nanostructures and nanodevices [Van17]. Nevertheless, the standard APT analysis of heterogenous systems still encounters several artefacts, due to for instance the non-stoichiometric evaporation and detection of different atomic species, non-ideal reconstruction algorithms for 3D volumes and differential laser light adsorption. Therefore more (fundamental) studies are required to bring APT up to the required accuracy and precision. In this work we specifically address the challenge of quantification accuracy and compositional profiling of Si x Ge 1-x compounds in thin films and the more complicated 3D devices (such as the gate-all-around (GAA) field-effect transistor, Fig A.), which are of high interest for future semiconductor applications (see e.g. [Mer17]).

Due to the dramatic downscaling of device features in recent technology nodes, characterizing the electrical properties of these structures is becoming ever more challenging as it often requires metrology able to probe local variations in dopant and carrier concentration with high accuracy. As no existing technique is able to meet all requirements, a correlative metrology approach is generally considered a solution. In this article, we study size-dependent effects on the dopant activation in nanometer-wide Si fins using a novel correlative approach. We start by showing that the micro four-point probe technique can be used to precisely measure the resistance of B doped and (laser) annealed Si fins. Next, we use transmission electron microscopy and scanning spreading resistance microscopy to show that the observed width dependence of the apparent sheet resistance of these fins can be explained by either a partially or a fully inactive region forming along the top of the fin sidewalls according to the annealing conditions.

In this study, we report the segregation of magnesium in the grain boundaries of magnesium-doped cuprous oxide (Cu2O:Mg) thin films as revealed by atom probe tomography and the consequences of the dopant presence on the temperature-dependent Hall effect properties. The incorporation of magnesium as a divalent cation was achieved by aerosol-assisted metal organic chemical vapour deposition, followed by thermal treatments under oxidizing conditions. We observe that, in comparison with intrinsic cuprous oxide, the electronic transport is improved in Cu2O:Mg with a reduction of resistivity to 13.3 ± 0.1 Ω cm, despite the reduction of hole mobility in the doped films, due to higher grain-boundary scattering. The Hall carrier concentration dependence with temperature showed the presence of an acceptor level associated with an ionization energy of 125 ± 9 meV, similar to the energy value of a large size impurity−vacancy complex. Atom probe tomography shows a magnesium incorporation of 5%, which is substantially present at the grain boundaries of the Cu2O.