One of the problems for current failure analysis in ULSI is that the flow from localization to physical analysis is not smooth due to decrease of device dimension and complicated device structure. Therefore we have developed a dedicated nano-probing system with FE-SEM to make the flow smooth by the identification and characterization of the exact failing transistor in advanced devices. In this report, items to be developed for high performance nano-probing system, such as optimum probe tip shape for probing on fine pattern, reduction of contact resistance for high reliability, increase of probe tip life time, precisely controlled probes and stage for finer geometry handling with high speed, load-lock chambers for sample and probe exchange and CAD navigation system for high throughput, 6 probes for extended applications, and probing controllers for easy operation like a manual probing system are described. Furthermore an actual failure analysis case (single bit failure in SRAM) using nano-probing system is also explained. The SEM based nano-probing system has been already applied to evaluation of 32 nm node devices and beyond.
With the rapid scaling down into nanoscale of LSI devices, the fabrication process becomes more and more difficult. Therefore, the requirement for 2D/3D high resolution and precise characterization are becoming high for the purpose of process control and also for understanding of device physics in nanoscale. One of the most important characterizations is the 2D profiling of charge carrier. Scanning spreading resistance microscopy (SSRM) is a typical 2D-profiling metrology, which is one of the applications of conductive atomic force microscopy(C-AFM). SSRM scans on a cross-sectional surface with conductive probe to measure the spreading resistance inside a device in nanoscale, obtaining the 2D-charge-carrier profiles in a short time. In this paper, we demonstrate the significant spatial resolution improvement of SSRM by decreasing of contact resistance between sample and probe with measuring in high vacuum. The fabrication process and measuring sequence of SSRM measurements are also explained. We also demonstrate the 1-nm spatial resolution of SSRM in carrier profiling by comparison with the 3-D device simulation. Applications to failure analysis of CMOSFETs clarified the impact of halo-carrier profiles on Vth-roll-off characteristics.
Atomic force microscopy (AFM) can be used not only as a tool for obtaining surface topography but also as a tool to investigate various electrical properties on semiconductor surfaces. It has been widely known that we can measure capacitance or spreading resistance using a conductive cantilever in contact to the sample surface. However, it is also possible to measure local electric properties such as surface potential or capacitance using dynamic-mode AFM. Recently, several researchers even succeeded in obtaining atomic-resolution surface potential images. In this paper, principles of the methods for investigation of local electric properties on semiconductor devices based on electrostatic force detection using dynamic-mode AFM are described. Current research trends in this research field and several examples of the local dopant profile measurement on semiconductor devices are also introduced.
In flash memory, both the “1” and “0” states are stored by changing the threshold voltage (Vth) of the transistor, where the Vth shifts are induced by stored charges. The metal-SiO2-SiN-SiO2-semiconductors (MONOS) memory stores charges in the SiN film of the gate SiO2-SiN-SiO2 (ONO) film. By using a scanning nonlinear dielectric microscopy (SNDM), we have succeeded in the identification of the charges (electrons and holes) concentrated areas in the ONO gate film in high-resolution. We also demonstrated that the SNDM has high performance and resolution for observing the charge distribution after program-erase operations cycling. Thus, it is expected that SNDM will be an effective method for observing the charges in the semiconductor devices. Finally, in downsized MONOS flash memory; we succeeded in visualizing the charge distribution by detecting a second-order nonlinear dielectric constant by using SNDM.
For the purpose of simultaneous electrical and optical characterization of light emission from individual nanostructures on semiconductor surfaces at the near-field, we developed a new microscope in which optical and electric excitation is combined into a single scanning tunneling microscope-based unit through the optical design of transparent probes. We describe the proof-of-concept measurements on GaAs and GaAs/AlAs heterostructures.
In eukaryotes, the actin cytoskeleton plays important roles in polarized cell growth and cytokinesis. Fission yeastis a model system for studying formation and role of actin cytoskeleton. Actin cytoskeleton in fission yeast cells forms patch, cable, and ring, which have been mainly observed by fluorescent microscopy. On the other hand, little is known about ultrastructures of actin cytoskeleton. Recently, we visualized the ultrastructure of these F-actin structures by high-pressure freezing and immuno electron microscopy. Furthermore, we clarified the directionality of F-actins forming the actin cytoskeleton in fission yeast cells. These results provide fundamental informations of actin cytoskeleton and insights into elucidating the functions.
Current standardization activities relating to the measurement and characterization of nanomaterials and nanostructures are described. The working items which have been discussed by WG2 of ISO TC229 on Nanotechnology are explained together with the scope and stracture of ISO TC229. Standardization strategy at the WG2 is also discribed.
To interpret core electron excitation spectra (energy-loss near edge structure: ELNES) obtained by electron energy-loss spectroscopy, it is necessary to compare the experimental ELNES with theoretical ones based on the first principle electronic structure calculations. To date a number of computer programs are open for public for the present purpose, so that even novice users are able to carry out theoretical calculations. In the present article, we introduce the fundamental principles for ELNES simulations, followed by summarizing the features and notice in use of the representative programs comparatively for discussing the chemical bonding states from the ELNES. Finally we show a case study, where theoretical ELNES for a metal oxide having different types of oxygen co-ordinations are calculated by several different methods introduced here and discuss their chemical bonding states of the real system.
The technique for measuring spatial distribution of X-ray attenuation coefficient is known as computed tomography. Recently, X-ray micro- and nanotomography techniques, which are sometimes combined with hard X-ray imaging microscopy, have been applied to the three-dimensional (3D) observations of micro- and nanoscopic features in materials. As is well known, the industrial X-ray tomography technique has been developed as well as that for medical diagnostic imaging. On the other hand, third-generation synchrotron radiation (SR) facilities such as the SPring-8 have been identified as an ideal source for X-ray tomography providing a high-energy X-ray beam with excellent lateral coherence and monochromaticity. Tomography performed utilizing SR facilities has enabled a reconstruction of volumes with the maximum spatial resolution of deep submicron level. Compared to the currently available other 3D visualization techniques, such as electron tomography, serial sectioning and neutron tomography, the X-ray tomography is clearly advantageous in the applicability to 4D (i.e. time being the fourth dimension with 3D space). The present authors have also proposed 3D/4D measurement procedures for various quantities, such as internal local crack driving force, 3D local stain and displacement fields, elemental concentration and crystallographic information, which would provide highly effective ways of assessing local phenomena quantitatively.
Ultrastructural distribution of membrane lipids has been difficult to observe by previous microscopic methods. By combining rapid freezing and freeze-fracture methods, we made it possible to capture membrane lipid distribution quantitatively at the nanoscale. The two-dimensional distribution of the molecules can be analyzed objectively by using several statistical methods. We applied this new technique to GM1 and phosphatidylinositol 4,5-bisphosphate and acquired several new findings.
Pathogenic bacteria, Mycoplasma form a membrane protrusion at a cell pole, bind to solid surfaces, and glide. Its mechanism is totally different from those of biomotility systems studied so far. The studies on the fastest species, Mycoplasma mobile are clarifying the machinery, component proteins, and mechanism. The gliding machinery is composed of 4 proteins, and supported from cell inside by a jellyfish-like cytoskeletal structure. The movement generated by ATP hydrolysis is transmitted to “leg” protein through “crank” protein on cell surface. The legs, string-like structures bind and pull sialic acids to one direction, and propel the cell forward.
Steroids synthesized in the nervous system de novo from cholesterol independently from peripheral endocrine glands are generally called “neurosteroids”. They are considered to exert the development, maturation, and differentiation of the brain. However, little is known about neurosteroid functions corresponding to specific structure and functions of the brain subregions. To understand functional significance, we have analyzed detailed expression and localization of steroidogenic enzymes in the brain. In this review, we have introduced localization of 5α-reductase, one of synthesizing enzymes of neurosteroids, in the olfactory bulb, which has been well characterized morphologically, and would like to show some results and discuss about potentially bioactive functions of neurosteroid.
Gap junctions are channel structures between cells and act as electrical synapses between neurons. Gap junctions are composed of “connexin” proteins. Connexins assemble as a hexameric transmembrane channel, connexon. We found morphological diversities of neuronal gap junctions in rodent retina by SDS-digested freeze-fracture replica immunogold labeling. They often showed string-, ribbon-, reticular- arrangements of connexons as well as typical plaque forms especially in the OFF sublamina of the inner plexiform layer. We also found that small gap junctions (<100 connexons) were abundant in the central nervous system, which were technically difficult to be detected by light microscopy or thin-sectioning electron microscopy. Double-replica labeling for Cx36 and Cx45 revealed that these two connexins made bi-homotypic gap junctions. The labeling for Cx36 and Cx45 were segregated in gap junction hemiplaques, and the segregation pattern was kept as same in the complementary side of hemiplaques.
In order to observed inner structure of power devices made of 4H-SiC, a new method named grazing incident synchrotron radiation topography was developed. This method is very suitable for the observation without any disturbance by contrast of lattice defects inside 4H-SiC wafers. The purposes of development of this method is to improve reliability of power devices and their yield ratio. We could obtained new information by the observation of inner structure of power devices, as well as by investigate their electrical properties. On a way of this work, on the other hand, it was identified that dislocations show very characteristic contrasts, and there are some rules among contrast of dislocations, their Burgers vectors, type of dislocations and directions of dislocations. We have discussed the origin of the characteristic contrast using dynamical theory of X-ray diffraction.
Low-k film has been adapted to LSI interconnects, although process-induced damage is still a serious problem. A technique to measure dielectric properties at nanometer-scale spatial resolution is required to improve device processes. Electron energy-loss spectroscopy with a transmission electron microscope (TEM-EELS) is a well-known technique to measure dielectric properties at nanometer-scale spatial resolution. It has previously only been applied to measure materials whose refraction factor was known. In this study, we developed a measurement technique using TEM-EELS that can be applied to a damaged layer in low-k material.
Neuronal Lewy body-like hyaline inclusions (LBHI) and astrocytic hyaline inclusions (Ast-HI) containing mutant superoxide dismutase 1 (SOD1) are morphological hallmarks of familial amyotrophic lateral sclerosis (FALS) associated with mutant SOD1. However, little is known that the mechanisms by which mutant SOD1 contributes to formation of LBHI/Ast-HI in FALS. Here, we show induction of LBHI/Ast-HI-like hyaline inclusions (LHIs) in vitro by ER stress in SK-N-SH cells. These LHI closely resemble LBHI/Ast-HI in patients with SOD1-linked FALS. LHI and LBHI/Ast-HI share the following features: 1)eosinophilic staining with a pale core, 2) SOD1, ubiquitin and ER resident protein (KDEL) positivity and 3) the presence of approximately 15–25 nm granule-coated fibrils, which are morphological hallmark of mutant SOD1-linked FALS. Moreover, in spinal cord neurons of L84V SOD1 transgenic mice at presymptomatic stage, we observed aberrant aggregation of ER and numerous free ribosomes associated with abnormal inclusion-like structures, presumably early stage neuronal LBHI. We conclude that the LBHI/Ast-HI seen in human patients with mutant SOD1-linked FALS may arise from ER dysfunction.