Hiromu Fujioka

Local field effects on voltage contrast in the scanning electron microscope

The local field effects on voltage contrast in the scanning electron microscope (SEM) mean that local fields generated by a non-uniform potential distribution on specimen surface cause a variation in the secondary electron (SE) detector current. It causes some errors in the voltage measurement. The authors present a theory to calculate the SE detector current in the presence of the local fields. In the calculation, they assume that the field distribution above the specimen surface (metal electrodes with 8 mu m width and 12 mu m separation) is two-dimensional. Analysed models are a conventional SEM detector system (model A), a retarding-field energy analyser with an extraction field (model B) and a high-resolution energy analyser with an extraction field (model C). The results show that the local field effects could not be neglected even in models B and C with strong extraction fields. The calculated values of local field effects in models A and B agree well with the experimental ones. The dependence of local field effects on the electrode geometry is equivalent to that on the extraction field, though this dependency is not so strong.

Rotation vector analysis of eye movement in three dimensions with an infrared CCD camera.

We have developed a new technique for analyzing the rotation vector of eye movement in three dimensions with an infrared CCD camera based on the following four assumptions; i) the eye rotates on a point; ii) the pupil edge is a circle; iii) the distance from the center of eye rotation to pupil circle remains unchanged despite the rotation; iv) the image of the eye by the CCD camera is projected onto a plane which is perpendicular to the camera axis. After taking digital images of voluntary circular eye movements, we first constructed a three-dimensional frame of reference fixed on the orbita of the subject wearing a goggle equipped with an infrared CCD camera, and determined the space coordinates of the center of eye rotation, the center of the pupil, and an iris freckle. We then took digital images of the eye movements during a saccade or vestibulo-ocular reflex (VOR) and analyzed the axis and angle of the eye movements by the trajectories of the center of the pupil and the iris freckle. Finally, Listings plane of saccade and the gain and the phase of VOR were obtained. The suitability of this technique is examined.

Analysis of the transit time effect on the stroboscopic voltage contrast in the scanning electron microscope

The transit time effect (TTE) on stroboscopic waveform measurements in the scanning electron microscope is analysed. Here the TTE means the voltage contrast variation due to the time-varying surface electric field near the measurement electrode. The results show that the TTE on waveform rise and fall times or amplitude measurements cannot be disregarded for waveforms with a time variation of the order of 100 ps or less. The TTE on pulse width measurements does not appear to be so large.

Generation and measurement of subpicosecond electron beam pulses

The generation and measurement of subpicosecond electron beam pulses by the transverse-longitudinal combination gate system is described. The temporal property of the pulse gate is analyzed with the help of the longitudinal emittance diagram. Close agreement has been obtained between the calculated pulse width and the observed one which was measured by the Lissajouss figure method. A beam pulse of 0.2 ps (FWHM) was produced.

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.

Gigahertz stroboscopy with the scanning electron microscope

The application of the stroboscopic scanning electron microscope to gigahertz Gunn effect devices is discussed. Two modes of operation, the deflection mode and the bunching mode, are considered. In the bunching mode, using 1.5 ps beam pulses, two-dimensional voltage contrast in a Gunn effect device triggered at 1 GHz has been observed. A powerful technique for a device in pulsed operation is also presented. With this technique, the nonuniform domain propagation in the three-dimensional-structure Gunn device in pulsed operation has been clearly observed. The duty cycle of the pulsed operation has been 4x10(-3).

Measurements of deep penetration of low-energy electrons into metal-oxide-semiconductor structure

A polycrystalline Si‐SiO2‐Si metal‐oxide‐semiconductor (MOS) transistor covered with thick insulation and passivation layers of SiO2 was examined to measure the threshold voltage shifts as a function of electron energy over the range of from 5 to 18 keV. The electron‐beam fluence was varied over six orders of magnitude from 2×10−9 to 2×10−3 C/cm2. From the experimental data, the fraction of the incident electron energy deposited in the gate oxide was determined. The result shows a deep penetration of low‐energy electrons beyond the electron range.

Measurements of the energy dependence of electron beam assisted etching of, and deposition on, silica

The electron beam assisted etch rates for SiO2 by using XeF2 and CF4 gases were measured as a function of primary electron energy. The deposition rate of Fe on SiO2 substrate with Fe(CO)5 as a source gas was also measured. It is seen that both the etch rate and the deposition rate are higher at lower primary electron energies in the region of 1 keV to 15 keV.

A new hemispherical retarding field energy analyser for quantitative voltage measurements in the SEM

A retarding field energy analyser for quantitative voltage measurements which functionally connects a uniform extracting field with a hemispherical analysing field is described. The design principles are : (i) the centres of the hemispherical grids are to be put on the virtual source from which the secondary electron seems to come straight ahead; (ii) the radii of the hemispherical grids are to be chosen as large as possible within a restricted working distance in a scanning electron microscope; (iii) all the analysed secondary electrons are to be collected. The accuracy of the voltage measurement has been improved by a factor of 10 compared with that in the plane-parallel retarding field energy analyser.

Dynamics of the Vestibulo-ocular Reflex in Patients with the Horizontal Semicircular Canal Variant of Benign Paroxysmal Positional Vertigo

Objective Two types of direction-changing positional nystagmus, the geotropic and apogeotropic variants, are observed in patients with the horizontal semicircular canal (HSCC) type of benign paroxysmal positional vertigo (H-BPPV). In this study, we assessed the dynamics of the vestibulo-ocular reflex (VOR) of the HSCC in patients with H-BPPV. Material and Methods Patients were rotated about the earth-vertical axis at frequencies of 0.1, 0.3, 0.5, 0.7 and 1.0 Hz with a maximum angular velocity of 50°/s. Eye movements were recorded on a video imaging system using an infrared charge-coupled device (CCD) camera, and our new technique for analyzing the rotation vector of eye movements in three dimensions was used. Results In the patients with geotropic positional nystagmus, there were no differences in VOR gain between rotation to the affected and unaffected sides at frequencies of 0.1–1.0 Hz. Although no differences in VOR gain at frequencies of 0.3–1.0 Hz were noticed in patients with apogeotropic positional nystagmus, the VOR gain at 0.1 Hz was significantly smaller on rotation to the affected compared to the unaffected side. Conclusion The results indicate that cupulolithiasis in the HSCC affected the dynamics of the HSCC-ocular reflex at 0.1 Hz, but not at higher frequencies, and that canalolithiasis in the HSCC does not change the VOR gain of the HSCC at any frequency. It is suggested that cupulolithiasis causes transient impairment of HSCC function by means of its mechanical restriction of movements of the cupula.