Electron Beam Induced Damage on Passivated Metal Oxide Semiconductor Devices

Electron beam testing of integrated circuits (IC) is currently based on the electron beam induced conductivity in insulators to short the passivation layer and to enable a voltage measurement at covered conductor tracks. However, applying this technique to passivated MOS devices causes severe radiation damage, which was at first explained by primary electrons penetrating into the deep-lying gate oxide. Nondestructive electron beam testing was expected by using low electron energies that do not allow the primary electrons to reach into the gate oxide. Therefore here the influence of nonpenetrating electron irradiation on the characteristics of passivated NMOS transistors has been studied. The experiments demonstrate that significant damage is caused even when primary electrons do not reach into the gate oxide. This can be explained by secondary X-rays, generated by the primary electrons in the upper layers, that then penetrate into the gate oxide. Radiation damage increases with irradiation dose, primary energy and with decreasing gate size. Though using the lowest primary electron energy possible to build up the necessary conductive channel, even low irradiation doses alter the devices drastically. Only by blanking off the high energy electron beam at gate oxide areas during the scan, i.e. by application of the window scan mode, is a nearly nondestructive testing of passivated MOS devices via the electron beam induced conductivity made possible. Another possibility to decrease radiation damage is the reduction of primary electron energy to about 1 keV. Then electron beam testing is no longer based on the physics of electron beam induced conductivity, but on the capacitive coupling voltage contrast

On the relation between maximum modulus, maximum term, and Taylor coefficients of an entire function

AbstractRelations are established between the quantities in the title in form of direct estimates, instead of measuring the growth of f by its order, type, or some generalized order. For entire functions of relatively slow growth, a distinct increase of precision is achieved. Our approach originates in work by Hadamard, Le Roy, Valiron, and Berg

Computer Simulation and Experimental Performance Data for an Electron Spectrometer for Electron Beam Testing of Integrated Circuits

Electron beam testing using voltage contrast in the scanning electron microscope has been established as a useful tool for nondestructive and nonloading functional testing and failure analysis of integrated circuits (IC). The accuracy of quantitative voltage measurements within the IC with the electron beam probe is determined by the performance of the secondary electron (SE) spectrometer used. For simulating the performance of SE-spectrometers a program-package has been developed by aid of which the voltage-and field-distributions within the spectrometers can be evaluated using a finite element method. Thus it is possible to trace electron trajectories throughout the spectrometer. By considering a great number of SE-trajectories, the detected integral SE-signal for different voltages at the IC can be determined as a function of the retarding field voltage within the spectrometer. In this way the performance of an existing spectrometer is simulated. The experimentally measured SE-signals are compared with the simulation data. This comparison showed that the program-package realistically simulates the spectrometer properties. Therefore this program-package enables an improvement of existing SE-spectrometers and in principle also the development of new spectrometer-assemblies. Here the suitability for optimizing a SE-spectrometer is shown

The translocation of transportin–cargo complexes through nuclear pores is independent of both Ran and energy.

AbstractActive transport between nucleus and cytoplasm proceeds through nuclear pore complexes (NPCs) and is mediated largely by shuttling transport receptors that use direct RanGTP binding to coordinate loading and unloading of cargo [1–4]. Import receptors such as importin β or transportin bind their substrates at low RanGTP levels in the cytoplasm and release them upon encountering RanGTP in the nucleus, where a high RanGTP concentration is predicted. This substrate release is, in the case of import by the importin α/β heterodimer, coupled directly to importin β release from the NPCs. If the importin β –RanGTP interaction is prevented, import intermediates arrest at the nuclear side of the NPCs [5,6]. This arrest makes it difficult to probe directly the Ran and energy requirements of the actual translocation from the cytoplasmic to the nuclear side of the NPC, which immediately precedes substrate release. Here, we have shown that in the case of transportin, dissociation of transportin–substrate complexes is uncoupled from transportin release from NPCs. This allowed us to dissect the requirements of translocation through the NPC, substrate release and transportin recycling. Surprisingly, translocation of transportin–substrate complexes into the nucleus requires neither Ran nor nucleoside triphosphates (NTPs). It is only nuclear RanGTP, not GTP hydrolysis, that is needed for dissociation of transportin–substrate complexes and for re-export of transportin to the cytoplasm. GTP hydrolysis is apparently required only to restore the import competence of the re-exported transportin and, thus, for multiple rounds of transportin-dependent import. In addition, we provide evidence that at least one type of substrate can also complete NPC passage mediated by importin β independently of Ran and energy

Acetylation of importin-α nuclear import factors by CBP/p300.

Histone acetylases were originally identified because of their ability to acetylate histone substrates 1, 2 and 3. Acetylases can also target other proteins such as transcription factors 4, 5, 6 and 7. We asked whether the acetylase CREB-binding protein (CBP) could acetylate proteins not directly involved in transcription. A large panel of proteins, involved in a variety of cellular processes, were tested as substrates for recombinant CBP. This screen identified two proteins involved in nuclear import, Rch1 (human importin-α) and importin-α7, as targets for CBP. The acetylation site within Rch1 was mapped to a single residue, Lys22. By comparing the context of Lys22 with the sequences of other known substrates of CBP and the closely related acetylase p300, we identified G/SK (in the single-letter amino acid code) as a consensus acetylation motif. Mutagenesis of the glycine, as well as the lysine, severely impaired Rch1 acetylation, supporting the view that GK is part of a recognition motif for acetylation by CBP/p300. Using an antibody raised against an acetylated Rch1 peptide, we show that Rch1 was acetylated at Lys22 in vivo and that CBP or p300 could mediate this reaction. Lys22 lies within the binding site for a second nuclear import factor, importin-β. Acetylation of Lys22 promoted interaction with importin-β in vitro. Collectively, these results demonstrate that acetylation is not unique to proteins involved in transcription. Acetylation may regulate a variety of biological processes, including nuclear import

Capacitive Coupling Voltage Contrast

Capacitive coupling voltage contrast (CCVC) allows electron-beam testing of passivated integrated circuits (IC) without radiation damage or prior, time-consuming specimen preparation. This effect occurs when low primary electron energies are used and the electron yield of the passivation layer is greater than 1. Signal changes in the relevant interconnections are transferred to the passivation surface via capacitive coupling, but they vanish there within the storage time due to electron irradiation. A physical model explains the dependence of CCVC on three parameters: electron irradiation, the passivation material and the signals within the IC. Computer simulations based on this model describe the experimentally-obtained dependencies of the storage time with precision and al low predictions to be made for using CCVC in electron beam testing. The requisite modifications to the electron beam testing system are described and the possible uses of CCVC for testing passivated devices within IC are demonstrated on the basis of examples

Atomic resolution dynamics of cohesive interactions in phase-separated Nup98 FG domains

Cohesive FG domains assemble into a condensed phase forming the selective permeability barrier of nuclear pore complexes. Nanoscopic insight into fundamental cohesive interactions has long been hampered by the sequence heterogeneity of native FG domains. We overcome this challenge by utilizing an engineered perfectly repetitive sequence and a combination of solution and magic angle spinning NMR spectroscopy. We map the dynamics of cohesive interactions in both phase-separated and soluble states at atomic resolution using TROSY for rotational correlation time (TRACT) measurements. We find that FG repeats exhibit nanosecond-range rotational correlation times and remain disordered in both states, although FRAP measurements show slow translation of phase-separated FG domains. NOESY measurements enable the direct detection of contacts involved in cohesive interactions. Finally, increasing salt concentration and temperature enhance phase separation and decrease local mobility of FG repeats. This lower critical solution temperature (LCST) behaviour indicates that cohesive interactions are driven by entropy

Two different subunits of importin cooperate to recognize nuclear localization signals and bind them to the nuclear envelope

AbstractBackground: Selective protein import into the cell nucleus occurs in two steps: binding to the nuclear envelope, followed by energy-dependent transit through the nuclear pore complex. A 60 kD protein, importin, is essential for the first nuclear import step, and the small G protein Ran/TC4 is essential for the second. We have previously purified the 60 kD importin protein (importin 60) as a single polypeptide.Results We have identified importin 90, a 90 kD second subunit that dissociates from importin 60 during affinity chromatography on nickel (II)–nitrolotriacetic acid–Sepharose, a technique that was originally used to purify importin 60. Partial amino-acid sequencing of Xenopus importin 90 allowed us to clone and sequence its human homologue; the amino-acid sequence of importin 90 is strikingly conserved between the two species. We have also identified a homologous budding yeast sequence from a database entry. Importin 90 potentiates the effects of importin 60 on nuclear protein import, indicating that the importin complex is the physiological unit responsible for import. To assess whether nuclear localization sequences are recognized by cytosolic receptor proteins, a biotin-tagged conjugate of nuclear localization signals linked to bovine serum albumin was allowed to form complexes with cytosolic proteins in Xenopus egg extracts; the complexes were then retrieved with streptavidin–agarose. The pattern of bound proteins was surprisingly simple and showed only two predominant bands: those of the importin complex. We also expressed the human homologue of importin 60, Rch1p, and found that it was able to replace its Xenopus counterpart in a functional assay. We discuss the relationship of importin 60 and importin 90 to other nuclear import factors.Conclusion Importin consists of a 60 and a 90 kD subunit. Together, they constitute a cytosolic receptor for nuclear localization signals that enables import substrates to bind to the nuclear envelope