IntroductionAtom probe tomography has primarily been used for atomic scale characterization of high electrical conductivity materials [1]. A high electrical field applied to needle-shaped specimens evaporates surface atoms, and a time of flight measurement determines each atom's identity. A 2-dimensional detector determines each atom's original position on the specimen. When repeated successively over many surface monolayers, the original specimen can be reconstructed into a 3-dimensional representation. In order to have an accurate 3-D reconstruction of the original, the field required for atomic evaporation must be known a-priori. For many metallic materials, this evaporation field is well characterized, and 3-D reconstructions can be achieved with reasonable accuracy.Compared with conventional atom probes, the use of a local electrode has been shown to increase the sustainable evaporation rate and field of view [2]. The localized electric field produced by the local electrode enables arrays of specimens to be analyzed, as opposed to a single, electropolished wire needle. Specimen arrays increase throughput by minimizing exchange to UHV and cryogenic temperatures, as well as increasing material statistics through analysis of many specimens. In order to take advantage of these specimen arrays, preparation techniques utilizing in-situ FIB liftout techniques were developed [3]. These techniques allow routine preparation of nominally 100nm diameter specimens. The FIB also enables much improved control of the specimen diameter so the atom probe experiments can be tuned accordingly.The maturation of local electrode and laser pulsed atom probe hardware, as well as FIB specimen preparation techniques, have enabled atom probe analysis of non-traditional materials such as semiconductors, ceramics, and some organic materials to become more commonplace [4]. For most of these materials, the evaporation field is not well characterized. For example, oxides and III-V materials tend to evaporate in clusters of atoms, rather than individual atoms [5]. The physics of cluster evaporation in atom probe experiments are not well understood, and the evaporation field required is also not well characterized. In order to increase the accuracy of the 3-D reconstructions in non-traditional materials, the evaporation field and its progression during an atom probe experiment should be calculated using the specimen geometric features, such as tip radius and shank angle.While a combination FIB and SEM can give some information about atom probe specimen structure, higher resolution characterization of specimens using TEM and STEM can further increase reconstruction accuracy. TEM can image not only the specimen radius and shank angle with higher precision, but also can give the internal structure of interfaces and precipitates. Diffraction and high resolution imaging can give information about the orientation of crystallographic axes with respect to the specimen, and thus allow accurate scaling of the reconstruction in the z-direction. Analyti...
The preparation of thinned lamellae from bulk samples for transmission electron microscopy (TEM) analysis has been possible in the focussed ion beam scanning electron microscope (FIB-SEM) for over 20 years via the in situ lift-out method. Lift-out offers a fast and site specific preparation method for TEM analysis, typically in the field of materials science. More recently it has been applied to a low-water content biological sample (Rubino 2012). This work presents the successful lift-out of high-water content lamellae, under cryogenic conditions (cryo-FIB lift-out) and using a nanomanipulator retaining its full range of motion, which are advances on the work previously done by Rubino (2012). Strategies are explored for maintaining cryogenic conditions, grid attachment using cryo-condensation of water and protection of the lamella when transferring to the TEM.
The development of the femtosecond laser (fs laser) with its ability to provide extremely rapid athermal ablation of materials has initiated a renaissance in materials science. Sample milling rates for the fs laser are orders of magnitude greater than that of traditional focused ion beam (FIB) sources currently used. In combination with minimal surface post-processing requirements, this technology is proving to be a game changer for materials research. The development of a femtosecond laser attached to a focused ion beam scanning electron microscope (LaserFIB) enables numerous new capabilities, including access to deeply buried structures as well as the production of extremely large trenches, cross sections, pillars and TEM H-bars, all while preserving microstructure and avoiding or reducing FIB polishing. Several high impact applications are now possible due to this technology in the fields of crystallography, electronics, mechanical engineering, battery research and materials sample preparation. This review article summarizes the current opportunities for this new technology focusing on the materials science megatrends of engineering materials, energy materials and electronics.
Laser delivery probes using multimode fiber optic delivery and bulk focusing optics have been constructed and used for performing materials processing experiments within scanning electron microscope/focused ion beam instruments. Controlling the current driving a 915-nm semiconductor diode laser module enables continuous or pulsed operation down to sub-microsecond durations, and with spot sizes on the order of 50 μm diameter, achieving irradiances at a sample surface exceeding 1 MW/cm2. Localized laser heating has been used to demonstrate laser chemical vapor deposition of Pt, surface melting of silicon, enhanced purity, and resistivity via laser annealing of Au deposits formed by electron beam induced deposition, and in situ secondary electron imaging of laser induced dewetting of Au metal films on SiOx.
Multiple new materials are being adopted by the semiconductor industry at a rapid rate for both semiconductor devices and packages. These advances are driving significant investigation into the impact of these materials on device and package reliability. Active investigation is focused on the impact of back-end-of-line (BEOL) processing on Cu/low-k reliability. This paper discusses Cu/low-k BEOL interfacial reliability issues and relates key items from the assembly process and packaging viewpoint that should be managed in order to prevent adverse assembly impact on BEOL interfacial reliability. Reliability failure mechanisms discussed include interface diffusion-controlled events such as the well-known example of Cu electromigration (EM), as well as stress-migration voiding. Interface defectivity impact on dielectric breakdown and leakage is discussed. Lastly, assessments of assembly impact on these Cu/low-k interfacial concerns are highlighted.
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