Katsumi Ura

Function testing of bipolar ICs and LSIs with the stroboscopic scanning electron microscope

The functional testing of individual circuits is essential for device manufacturers when integrated circuits have not satisfied design specifications. What is required for the functional testing of modern high-density and fast IC and large scale integration (LSI) circuits is a method which has a time resolution in the subnanosecond region and a spatial resolution in the submicrometer region. Furthermore, the test probe must be easy to position on the circuit, and inspection should be possible without having to remove the passivation glass oxide. The authors show that all of these requirements can be satisfied by using a scanning electron microscope (SEM) in the stroboscopic voltage contrast mode. A microcomputer-controlled SEM allows the testing of internal circuit operations with a time resolution of 0.2 ns, a spatial resolution of 0.2 /spl mu/m, and a voltage resolution of 50 mV. Application to a bipolar hex-inverter IC, a quadruple-multiplexer IC, and a 1024 bit PROM in the megahertz region is reported to demonstrate the efficiency of the system.

Utilizing the charging effect in scanning electron microscopy.

The charging effect of an insulating specimen from electron beam (e-beam) irradiation may be utilized to facilitate imaging in the scanning electron microscope (SEM). This has been confirmed by a great deal of experimental work during the last three decades. Particularly, recent investigations indicate that even located underneath insulating thin films that a low energy e-beam cannot penetrate, conductors not biased and overlay marks, are observable through a novel imaging pattern, charging contrast. Unlike conventional SEM contrasts, which usually reflect surface characteristics, the dynamic charging contrast can reveal information of underlying structures without any external exciting signal. The authors consider that this kind of charging contrast arises from the different redistribution rates of secondary electrons returning to the surface under the surface local field of the charged specimen. The charging contrast has the prospect of extending the SEM application and forming new testing methods matched with the fast development of integrated circuits.

Transient analysis of Cockcroft-Walton cascade rectifier circuit after load short-circuit

Abstract On the basis of simulation results, analytical solutions of the transients in the main and branch discharging routes in a Cockcroft-Walton cascade rectifier circuit, in responce to a load short-circuit discharge, are derived. Using these analytical expressions, transient currents, energy dissipation in the circuit elements and the effects of circuit parameters on transients are investigated quantitatively for the first time. Results show that the diodes at the uppermost and lowest ends suffer stronger surges; inserting resistors and inductors into the circuit can weaken the undesirable effects of a surge on circuit elements.

Measurement of Surface Vacuum Potential from the Energy Spectrum of the Secondary Electron in the Scanning Electron Microscope

A measurement method for determining the contact potential between the specimen and the analyzer from an S-curve (an integrated curve of secondary electron energy distribution) in the scanning electron microscope is described. The measured S-curve is best-fitted to the calculated S-curve assuming the secondary electron energy distribution and the instrumental function of the analyzer. The work function of the retarding electrode in the analyzer was calibrated by the use of thermionic emission from a heated W filament. The work function of acid-cleaned Cu was 4.71 V, while that of untreated Al was 3.64 V. It is shown that the previously reported charging characteristics of an electrically floating gate in the MOS structure under electron beam irradiation are well explained by taking account of the surface vacuum potentials. The work function of insulator SiO2 was estimated to be on the order of 7 V.

Nanosecond Stroboscopic Electron Spectroscopy for Observation of Nuclear Excitation by Electron Transition (NEET) in 197Au

Electron transitions to inner atomic shells release their excess energies in the form of X-rays or Auger electrons. In addition to these two usual processes, a third mechanism called nuclear excitation by electron transition (NEET) can participate in the de-excitation process of atomic inner-shell ionization, if the NEET conditions, in which the nuclear and electronic transitions have almost equal transition energies and a common multipolarity, are satisfied. To observe NEET in 197Au, which would emit 63 keV internal conversion electrons with a half-life of 1.9 ns as a consequence of the NEET process, a specially designed stroboscopic electron spectrometer system was developed. The system allows us to observe the time spectrum of conversion electrons with a time resolution of subnanoseconds.

SUPPRESSING OSCILLATIONS OF ZENER DIODE IN AN ULTRAHIGH-VOLTAGE ELECTRON MICROSCOPE

Even in the low‐current region of some high‐voltage applications, e.g., in electron microscopes, a Zener diode may cause unwanted oscillations due to negative resistance. An effective method to suppress the oscillations is presented. In this method a series resistor and a parallel capacitor are connected with the Zener diode. The former can eliminate relaxation oscillation due to external capacitance and the latter can smooth parasitic oscillations.