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Acta materialia 253, 118961 (2023). doi:10.1016/j.actamat.2023.118961, In order to obtain a fundamental understanding of the phenomena accompanying thermomechanical fatigue of Cu metallization used in power electronics, as well as the resulting deterioration of electric properties, there is a need to assess intragranular microstructure and strain evolution within individual Cu grains and near grain boundaries. Here, synchrotron dark field X-ray microscopy (DFXM) is used to characterize as-deposited and 5 × 104 times thermally-cycled 20 µm thick Cu films. The cycling was performed using a dedicated test chip in the range of 100–400 °C applying a heating rate of 106 K/s. The thermomechanical treatment results in severe shear deformation of Cu grains, film surface roughening, gradual grain microstructural refinement, the emergence of microscopic voids preferably at high angle grain boundaries (HAGBs) and finally in the voids' percolation, as revealed by in-situ and ex-situ scanning electron microscopy. DFXM provides experimental evidence that mosaicity of Cu grains, residual tensile and compressive elastic strain concentrations and full width at half maximum of Cu 111 reflections increase simultaneously in the vicinity of the HAGBs. The latter is interpreted as resulting from vacancy condensation in front of the HAGBs, after dislocations have moved across cycled grains and partly annihilated. Moreover, the observed HAGB decohesion and gradual void formation are correlated with the supposed hardening of regions near HAGBs, which thus lose their ductility during cyclic elasto-plastic deformation. The results are complemented with the ex-situ X-ray nanotomography data, which document the voids' percolation across the film's thickness with a “crack” width of up to ∼2 µm. In general, the study identifies the inhomogeneous intragranular microstructural refinement and a gradual condensation of structural defects near HAGBs as driving forces for void formation in thick Cu metallizations during fast thermo-mechanical fatigue., Published by Elsevier Science, Amsterdam [u.a.]

Focused Ion Beam (FIB) systems can be used to generate controlled micro- and nano-features on a solid surface. Prediction of surfaces fabricated in this way requires knowledge of the rate of removal of the target material in order to simulate the evolution of the surface. In this paper we present a continuous-time model of this process that allows us to predict the shape of trenches and freeform surfaces under the action of FIB. This type of model is appropriate when the points that describe the discrete trajectory of the beam (the line connecting consecutive dwell points) are close enough that the craters generated on the surface overlap. In the case of a straight beam path with constant dwell time, a trench of uniform depth is generated under these conditions. This simplified approach considerably reduces the computing time needed to simulate the process, without significantly reducing the accuracy of the predicted surface. Calibration of the model for a particular FIB setup and workpiece involves only a small number of experimental trials. The predictions of the model have been tested on a single crystalline Boron p-doped Si target material for several different beam paths. The depth and shape of the cross section of single and overlapping trenches with constant dwell time are predicted with high accuracy. The model was also used to predict three freeform surfaces, where the dwell time varies along each line of the beam path. Atomic force microscopy topography measurements show that the average relative error between the measured and simulated profiles is 2–10% depending on the complexity of the machined surface.

Scanning probe microscopy techniques and, in particular, scanning spreading resistance microscopy (SSRM) were used for a detailed characterization of focused ion beam (FIB) induced damage in the surrounding of purposely irradiated areas on silicon. It is shown that the damaged area detected using these techniques extends up to several micrometers around the irradiated structures. The influence of the key FIB processing parameters on the FIB induced damage was examined. Parameters which were taken into account are the ion dose (from 1012 to 1018 cm−2), the milled structure size (circle diameters from 0.25 to 10 µm), the beam energy (from 10 to 30 keV), and the beam current (from 1.5 to 280 pA). Moreover, the influence of the SSRM settings on the measurement results was investigate d. Settings which were considered are the bias voltage and the force applied to the tip during the SSRM analysis. High resolution transmission electron microscopy and secondary ion mass spectroscopy analyses were performed to validate the SSRM results. Scattering between Ga ions and residual gas particles in the vacuum chamber of the FIB tool is identified as the main reason for the observed damaged area.

Scanning spreading resistance microscopy (SSRM) has been applied to study focused ion beam (FIB) induced damage in silicon in dependence on ion irradiation doses from 1012 cm-2 to 2·1016 cm-2. Starting from the lowest dose, SSRM detects increasing spreading resistance (SR) with increasing dose. For doses from 2·1013 cm-2 to 4·1014 cm-2, a slight decrease of SR is measured whereas for higher doses SR again slightly increases. The results are explained by physical effects like decreased carrier mobility due to increased scattering, amorphisation of silicon and precipitation of implanted Ga ions. The results clearly prove that SSRM is well suited for the fast detection of ion beam induced damage with high lateral resolution.