Two-dimensional (2D) transition metal dichalcogenides (TMDCs), such as molybdenum disulfide ( MoS 2 ), have significant potential as materials for the next generation of flexible electronics. They offer advantages over conventional semiconductors, particularly due to their tunable crystal phases. However, precise control of phase transformation in 2D layers deposited using low-temperature processes in a bottom-up approach for future electronics has not yet been mastered, which limits their integration into scalable device technology. This study demonstrates the control of the phase composition of plasma enhanced atomic layer deposited (PEALD) MoS 2 films by direct writing with focused Li + and Ga + ion beams, and retransformation into the 2H phase by ultrashort pulse laser processing. The ion beam-treated films exhibit excellent long-term stability and are therefore suitable for industrial processes.

Inverse analysis from indentation experiments has been a challenging problem due to the nonlinear relationship between indentation response and material parameters. In this work, a data-driven method is proposed that integrates an artificial neural network (ANN) and evolutionary optimization for the reliable and efficient inverse parameter identification. A large dataset is generated by simulating the indentation process based on different combinations of material parameters in a systematic way. Then, by using the simulated data, a set of ANN models is trained that can efficiently predict the indentation responses, i.e., the displacement-time curve, the indentation force, and the surface profile, as a function of material parameters. These trained models exhibit the potential to replace the computationally expensive numerical simulations for the identification of material parameters by inverse analysis. In this way, the surrogate models make the numerical evaluation of the loss function, which is minimized during the inverse analysis, orders of magnitude faster. This enables the use of the powerful genetic algorithm for the minimization of the loss function, which would be impossible without numerically efficient surrogate models, as this algorithm requires many iterations to produce robust results. In this work, we systematically investigate which mathematical loss function leads to robust and unique results in determining the material parameters through inverse analysis of indentation results. The results show that such an inverse analysis can be successfully performed for simulation data. In forthcoming work, this method will be generalized to experimental indentation data, which will allow the characterization of the mechanical behaviour of materials by micro- or nano-indentation tests.

Over the past three decades, nanoindentation has continuously evolved and transformed the field of materials mechanical testing. Once highlighted by the groundbreaking Oliver–Pharr method, the utility of nanoindentation has transcended far beyond modulus and hardness measurements. Today, with increasing challenges in developing advanced energy generation and electronics technologies, we face a growing demand for accelerated materials discovery and efficient assessment of mechanical properties that are coupled with modern machine learning-assisted approaches, most of which require robust experimental validation and verification. To this end, nanoindentation finds its unique strength, owing to its small-volume requirement, of fast-probing and providing a mechanistic understanding of various materials. As such, this technique meets the demand for rapid materials assessment, including semiconductors, ceramics, and thin films, which are integral to next-generation energy-efficient and high-power electronic devices. Here, we highlight modern nanoindentation strategies using novel experimental protocols outlined by the use of nanoindentation for characterizing functional structures, dislocation engineering, high-speed nanoindentation mapping, and accelerating materials discovery via thin-film libraries. We demonstrate that nanoindentation can be a powerful tool for probing the fundamental mechanisms of elasticity, plasticity, and fracture over a wide range of microstructures, offering versatile opportunities for the development and transition of functional materials.

Diatoms are widely studied biological objects because of their large variety of geometric shapes and their unique physical and chemical properties. They survive widely in nature within moisture. Imaging the diatoms three dimensionally in moisture and correlating their mechanical behavior is an interesting and challenging topic. Here, the morphology and mechanical properties of diatoms were studied in wet state and then in dry state. A customized sample holder was integrated into a laboratory transmission X-ray microscope to image the morphology changes and volume shrinkage of the diatom while transitioning from the wet to the dry state. The measured volume shrinkage of a single diatom cell of Actinocyclus sp. is about 0.16. By performing an in-situ micromechanical experiment in both states, the maximal loading force of a single Actinocyclus sp. was determined until cracking appeared and compared in both states. This value is in the range of several hundred µN in the wet state and single-digit mN in the dry state. The normalized stiffness of the studied diatoms is significantly higher in the dry state than in the wet state. 2D radiograph and 3D tomography imaging of the diatoms reveal the different locations for crack propagation in both states. Our study supplies the important imaging method, the structure and functional information of the diatoms for future studies on diatoms in moisture but also in dry state. This information can help design bio-inspired materials and even in the development of bio-sustainable materials.

2D polymers have emerged as a highly promising category of nanomaterials, owing to their exceptional properties. However, the understanding of their fracture behavior and failure mechanisms remains still limited, posing challenges to their durability in practical applications. This work presents an in-depth study of the fracture kinetics of a 2D polyimine film, utilizing in situ tensile testing within a transmission electron microscope (TEM). Employing meticulously optimized transferring and patterning techniques, an elastic strain of ≈6.5% is achieved, corresponding to an elastic modulus of (8.6 ± 2.5) GPa of polycrystalline 2D polyimine thin films. In step-by-step fractures, multiple cracking events uncover the initiation and development of side crack near the main crack tip which toughens the 2D film. Simultaneously captured strain evolution through digital image correlation (DIC) analysis and observation on the crack edge confirm the occurrence of transgranular fracture patterns apart from intergranular fracture. A preferred cleavage orientation in transgranular fracture is attributed to the difference in directional flexibility along distinct orientations, which is substantiated by density functional-based tight binding (DFTB) calculations. These findings construct a comprehensive understanding of intrinsic mechanical properties and fracture behavior of an imine-linked polymer and provide insights and implications for the rational design of 2D polymers.

Metallization structures in microelectronic systems undergo various degradation processes. They can be caused by diffusion mechanisms induced by electrical current only or by electrical current in combination with different boundary conditions like parallel thermo-mechanical strains or specific loading cycles in the currents itself. Beyond that, solely thermo-mechanical strain cycles can lead to a fatigue-based degradation of the microelectronics metallization. All those mechanisms can lead to a degradation in performance and ultimately to failures in the microelectronic systems. To physically understand these degradation processes, to formulate appropriate lifetime models, and to mitigate degradation with more robust designs, the failure mechanisms need to be studied in detail. Most crucial to that is an advanced actuation, analysis and monitoring of the development of the failure peculiarities over time using novel and improved accelerated testing procedures. For example, a novel setup for low frequency pulsed-current electromigration (EM) testing will be shown in conjunction with the needed advanced PFA methods. There, the non-equilibrium Joule-heating thermal fields lead to a degradation behavior different to the one expected by just the current duty cycles.

High-quality patterning determines the properties of patterned emerging two-dimensional (2D) conjugated polymers which is essential for potential applications in future electronic nanodevices. However, the suitable patterning method for 2D polymers is yet concluded because it’s still challenging to gain comprehensive understanding of their damage mechanisms by visualizing the structural modification during patterning process. Here, the damage mechanisms during patterning of 2D polymers, induced by various patterning methods, are unveiled based on a systematic study of structural damage and edge morphology on an imine-based 2D polymer (polyimine). Patterning using focused electron beam, focused ion beam (FIB) and mechanical carving is evaluated. Focused electron beam successively introduces sputtering effect, knock-on displacement damage and massive radiolysis effect as increasing the electron dose from 9.46×107 e-/nm2 to 1.14×1010 e-/nm2. The successful pattering is enabled by knock-on damage while impeded by carbon contamination when beyond a critical sample thickness. FIB creates current-dependent edge morphologies and extensive damage from the ion implantation caused by the tail of unfocused beam. A precisely controlled tip can tear the polyimine film through grain boundaries and in hence create the patterning edge with suitable edge roughness for certain application senarios when the beam damage is avoided. Taking structural damage and the resulting quantitative edge roughness into consideration, this study provides a detailed instruction on the proper patterning techniques for 2D crystalline polymers and paves the way for tailored intrinsic properties and device fabrication using these novel materials.

High-resolution imaging of Cu/low-k on-chip interconnect stacks in advanced microelectronic products is demonstrated using full-field transmission X-ray microscopy (TXM). The comparison of two lens-based laboratory X-ray microscopes that are operated at two different photon energies, 8.0 keV and 9.2 keV, shows a contrast enhancement for imaging of copper nanostructures embedded in insulating organosilicate glass of a factor of 5 if 9.2 keV photons are used. Photons with this energy (Ga-Kα radiation) are generated from a Ga-containing target of a laboratory X-ray source applying the liquid-metal-jet technology. The 5 times higher contrast compared to the use of Cu-Kα radiation (8.0 keV photon energy) from a rotating anode X-ray source is caused by the fact that the energy of the Ga-Kα emission line is slightly higher than that of the Cu-K absorption edge (9.0 keV photon energy). The use of Ga-Kα radiation is of particular advantage for imaging of copper interconnects with dimensions from several 100 nm down to several 10 nm in a Cu/SiO2 or Cu/low-k backend-of-line stack. Physical failure analysis and reliability engineering in the semiconductor industry will benefit from high-contrast X-ray images of sub-μm copper structures in microchips.

The semiconductor industry is continuing the scaling down of both device and on-chip interconnect features, for performance and economic reasons. This trend has implications for the design of guard ring structures, i.e. metallic non-functional structures in the back-end-of-line (BEoL) stack designed to be efficient to stop microcracks. In this work, we present a sample design for an in situ experiment to study mechanical degradation and failure mechanisms of crack stop structures in the BEoL stack, to ensure the mechanical robustness of microchips for future technology nodes. Additional finite element method (FEM) simulations provide supplementary understanding of the crack kinetics. To examine the effects of mechanical loading on crack stop elements of the BEoL stack, a novel sample geometry for an in situ fatigue experiment using x-ray microscopy was developed. The x-ray microscope (ZEISS Xradia 800 Ultra) enables high-resolution imaging of the 3D-patterned sample structures and defects such as microcracks. The tailored sample geometry allows the application of a tensile load to a BEoL specimen by a lever mechanism. The feasibility of the sample design is shown by mode-I loading of a pure interconnect sample. Post-mortem analysis by scanning electron microscopy (SEM), confirming planar microcrack propagation from the notch through the dielectric layer with small deflections of the crack path near cone shaped copper vias. FEM simulations focusing on the stress-strain fields around a crack tip indicate the beginning of copper plasticity as major mechanism starting the redirection of cracks due to resulting material compression in front of the obstacle.

Metallization structures in microelectronic systems undergo various degradation processes. They can be caused by diffusion mechanisms induced by electrical current only or by electrical current in combination with different boundary conditions like parallel thermo-mechanical strains or specific loading cycles in the currents itself. Beyond that, solely thermo-mechanical strain cycles can lead to a fatigue-based degradation of the microelectronics metallization. All those mechanisms can lead to a degradation in performance and ultimately to failures in the microelectronic systems. To physically understand these degradation processes, to formulate appropriate lifetime models, and to mitigate degradation with more robust designs, the failure mechanisms need to be studied in detail. Most crucial to that is an advanced actuation, analysis and monitoring of the development of the failure peculiarities over time using novel and improved accelerated testing procedures. For example, a novel setup for low frequency pulsed-current electromigration (EM) testing will be shown in conjunction with the needed advanced PFA methods. There, the non-equilibrium Joule-heating thermal fields lead to a degradation behavior different to the one expected by just the current duty cycles.

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High-resolution imaging of buried metal interconnect structures in advanced microelectronic products with full-field X-ray microscopy is demonstrated in the hard X-ray regime, i.e., at photon energies > 10 keV. The combination of two multilayer optics—a side-by-side Montel (or nested Kirkpatrick–Baez) condenser optic and a high aspect-ratio multilayer Laue lens—results in an asymmetric optical path in the transmission X-ray microscope. This optics arrangement allows the imaging of 3D nanostructures in opaque objects at a photon energy of 24.2 keV (In-Kα X-ray line). Using a Siemens star test pattern with a minimal feature size of 150 nm, it was proven that features < 150 nm can be resolved. In-Kα radiation is generated from a Ga-In alloy target using a laboratory X-ray source that employs the liquid-metal-jet technology. Since the penetration depth of X-rays into the samples is significantly larger compared to 8 keV photons used in state-of-the-art laboratory X-ray microscopes (Cu-Kα radiation), 3D-nanopattered materials and structures can be imaged nondestructively in mm to cm thick samples. This means that destructive de-processing, thinning or cross-sectioning of the samples are not needed for the visualization of interconnect structures in microelectronic products manufactured using advanced packaging technologies. The application of laboratory transmission X-ray microscopy in the hard X-ray regime is demonstrated for Cu/Cu6Sn5/Cu microbump interconnects fabricated using solid–liquid interdiffusion (SLID) bonding.

The combination of analog/mixed-signal, high-voltage and embedded non-volatile memory options with sensor and actuator integration is still common in automotive, industrial, communication and medical applications. MEMS with or without integrated CMOS, 3D integration micro transfer printing and integrated microfluid systems are in use to realize such applications. The established top metal interconnect materials for analog/mixed-signal CMOS applications are thick Aluminum (AlCu with Titan and Titanium Nitride) and thick Copper. Integrated noble metal electrodes are necessary for MEMS applications like microfluidics. The reliability requirements of a CMOS/ MEMS process differs from a long storage shelf life at room temperature, long life time for medical (in-body) or space applications up to high operating conditions for automotive and industrial applications like oil drilling. Applications, like functional surfaces, combine integrated circuits for example for next generation DNA sequencing. The noble metals for electrodes on top are thinner for such applications. An additional reliability challenge for such a lab on a chip is corrosion. Automotive applications have often mission profiles which need high currents, high temperature and a growing mechanical stability. The reliability of noble top metals is more and more under investigation because MEMS are more common in automotive products. The knowledge about reliability especially about mechanical properties is an interesting topic in addition to the results from standard tests like electro migration and stress migration tests because of the advanced mechanical stress in the applications and the danger of corrosion. The comparison of the electromigration performance and mechanical stability of AlCu, Copper, Gold and Platinum as thick and/ or top metal tracks is necessary to evaluate and assess the suitability of the materials for the different applications. The possibilities to generate test results for thick and or noble metals are limited because of the necessary long test times for thick metals and materials like Gold or Platinum. The interaction of different failure mechanisms and the different material and stack combinations of the CMOS part make an assessment difficult. Simulations can support the choice of materials by values for mechanical stress and stress divergences as well as they can deliver basic knowledge about the main failure mechanisms. Only a smaller number of varying interconnect stacks will be realized in a development of a new process. The basic knowledge from simulation results will help to decide about the type of reliability test and test effort for the process qualification.

On-chip interconnect stacks (Back End of Line, BEoL) in modern heterogeneous microelectronic products are exposed to various micromechanical loads. Each can lead to different failure modes of the whole system. To locally probe the micromechanical robustness of BEoL stacks, it is necessary to precisely control the mechanical loading conditions there. Three micromechanical BEoL robustness evaluation designs are presented, enabling a load and failure mode-adapted damage induction and identification. Those enable to test BEoL structures below and in the vicinity of Cu-pillars in compression, shear, and tensile mode. Acoustic Emission sensing capabilities are implemented to detect the very early stages of mechanical failures.

A novel experimental setup for testing interface properties of single copper interconnect structures is presented. The method is based on in-situ SEM nanoindentation experiments, utilized to probe customized copper structures manufactured by the Dual Damascene process. In this way the testing structures resemble product-like length-scales and properties. For the investigation of interface properties, the experimental load-displacement data is reviewed. Focused ion beam (FIB) cross sections are performed to validate the delaminated interface. FEM-simulations, based on the measured load-displacement data are used to determine the stress state in the test structures and to derive values for the interface fracture strength of the investigated interface.

For micromechanical robustness evaluation methods, it is advantageous if the mechanical loading conditions applied can be controlled as precisely as possible. For microchips, this is required to determine the robustness under specific conditions, e.g. during assembly or characteristic application/usage scenarios. In this work, three different micromechanical BEoL (Back End of Line) robustness evaluation methods are presented which should enable a more precise and flexible mechanical load induction and damage identification. They have been subsequently developed. Three main aspects characterize the customization of the developed approaches:•The design and testing of customized micro-tools to precisely apply mechanical load to individual Cu-pillars.•The implementation of an AE (Acoustic Emission) monitoring approach to detect minor damages during mechanical loading. This strategy also enabled the development of sub-critical loading experiments for which AE signals served as a damage indicator and mechanical loading was aborted upon the detection of AE events.•The development of a new measurement setup and approach to enable the solder attach of individual Cu-pillars to a mechanical testing system. The applications of these approaches should enable the induction of customized mechanical loading conditions and the identification of failure modes and damage initiation locations.

This study presents a novel approach of micromechanical interfacial testing in loading mode III. The interfaces beneath single copper interconnect structures are investigated. The method is based on lateral nanoindentation experiments, utilized to probe customized copper torsion structures manufactured by the Dual Damascene process. Thus, the test structures resemble product-like length-scales and properties. For the investigation of interface properties, the experimental load-displacement data were reviewed. Two different interfaces occurring in Back End of Line (BEoL) structures are probed: Copper to Ta/Ta-N barrier as well as Copper to Si-N. SEM images and FIB cross-sections are performed, validating the delamination of the targeted interface. While the first interface shows a very high strength and cannot be delaminated by the here presented experiments, the latter one was brought to delamination in mode III several times. The tests yielded reproducible load-displacement data, the load at delamination for the interface Copper to Si-N was measured to be 130 & PLUSMN; 40 & mu;N. A simple analytical approximation for the maximum shear stresses applied in mode III at the interface of interest is provided. The proposed testing approach is able to reproducibly manufacture and test large quantities of the reality like test structures, while avoiding time-consuming FIB based preparation routines. This can help to evaluate the interface properties in modern BEoL stacks and could lead to simulation based design improvements.

The sub-microstructure of polycrystalline lithium nickel manganese cobalt oxide (Li[NixMnyCo1−x−y]O2, abbr. NMC) secondary particles is determined by the arrangement, morphology and crystallographic orientation of the primary particles and strongly impacts their capacity, rate capability and aging. Although most electrochemical models do not resolve the sub-microstructure, understanding the relationship between a secondary particle’s sub-microstructure and its electrochemical behavior is essential for the rational design of advanced secondary particles. In this paper we investigate the sub-microstructure of polycrystalline NMC secondary particles both experimentally and computationally. Experimentally, electron backscatter diffraction (EBSD) measurements characterize the crystallography of the primary particles and a radial orientation of the a-b diffusion planes of the individual atomically layered Li[Ni0.6Mn0.2Co0.2]O2 (NMC622, Ni-rich) primary particles, revealing a Gaussian distribution. Computationally, three-dimensional electrochemical simulations of polycrystalline secondary particles model the impact of the crystallographic orientation of the primary particles on the secondary particle’s capacity. These simulations predict that the investigated NMC secondary particles have a capacity at a discharge rate of 1C that is up to 8% higher than that of a randomly oriented material. This shows that the crystallographic orientations of polycrystalline secondary particles have a severe impact on the utilization of NMC particles.

The application of virtual evaluation tools based on the Finite Element Method (FEM) is already widespread in the field of electronics. To predict the lifetime and reliability of microelectronic devices as well as the stress evolution for certain application conditions, fully parametrized finite element studies are utilized. At the assembly level, the geometries and material properties of these models are required to be provided as very complex and predominantly non-linear data. Thus, the predictive power of these models rely on the precisely measured thermo-mechanical properties of the involved materials, for instance the viscoelastic behavior of polymers used in underfillers, PCBs, adhesives, or mold layers. To that, this study focusses on the viscoelastic behavior and its characterization techniques. It is always challenging to determine the relevant viscoelastic properties on product-identical size ranges and specimens. To address this challenge, in this paper, macroscopic and microscopic variants of the Dynamical Mechanical Analysis (DMA) technique are applied to identical, IC product-relevant polymer samples to compare the results of both approaches as well as highlight their corresponding strengths. To directly compare the two DMA techniques, they are both applied to identical dog bone samples, prepared for the macroscopic DMA.

Under harsh application conditions in fields such as aerospace or automotive, it is crucial that the mechanical robustness of microchip components is ensured at any time. To obtain this, thorough and highly specialized testing approaches have to be deployed already in the design phase. The general strategy of these approaches is to induce (thermo-)mechanical load to a given system or component under well controlled conditions and assess the resulting effects. The testing methods should emulate the mechanical application conditions as closely as possible to identify the most damage prone areas of the system and to obtain an understanding of the occurring damage processes. In this work, the development and deployment of two different testing methods to evaluate mechanical BEoL (Back end of Line) stack robustness by inducing micromechanical load to superjacent Cu-pillars are introduced. In flip chip applications, Cu-pillars are immobilized by a solder connection as well as underfill material. Compared to previously developed methods, it was attempted to realize mechanical scenarios which are closer to assembly or application conditions. Therefore, the methods presented in this work can be regarded as subsequent developments of e.g. the Cu-pillar shear-off approach presented in Silomon et al. (2021). The details are discussed in more depth in Silomon et al. (2022). Specifically, a mechanical immobilization approach utilizing an indenter tip with a cavity was developed as well as a soldering approach utilizing a Cu indenter tip as a soldering bolt and a landing pad simultaneously. The approaches were deployed on a high-end microchip sample which has been introduced and investigated in Silomon et al. (2021). Two different mechanical loading conditions were emulated utilizing the developed approaches. These conditions are relevant at different points in the life cycle of a microchip and could not be induced utilizing previously developed methods. Oscillating load as an emulation of thermal expansion and contraction or vibration (application conditions) as well as tensile loading as an emulation of assembly conditions were induced. Applying mechanical load to individual Cu-pillars utilizing the different methods enabled the determination of the failure conditions and subsequent analysis led to the identification of the respective damage mode. Additionally, sub-critical experiments utilizing AE (acoustic emission) signal monitoring as a damage indicator were conducted to determine the exact location of damage initiation. This was achieved by subsequent damage assessment measurements utilizing optical microscopy, nXCT as well as SEM/FIB analyses. Applying this workflow, it was possible to describe the damage modes as well as to identify the most damage prone areas for the specific loading conditions induced by the two different developed mechanical loading methods.