Hideo Todokoro

Role of Ion Bombardment in Field Emission Current Instability

The role of ion bombardment in field emission current instability is clarified experimentally by varying the emission current level and pressure over a wide range. It is found that bombarding ions sputter-off adsorbed gas molecules on the emitter surface and this causes field emission current fluctuation. This current fluctuation caused by ion bombardment is larger than that caused by gas molecule migration when the product of the pressure and the emission current is higher than 7×10-12 PaA. The relative fluctuations turn out to be the logarithm of the product of the pressure and the emission current. The ions are mainly generated close to the emitter due to electron collisions with residual gas.

Electron‐beam cell‐projection lithography system

An electron‐beam exposure system HL‐800D has been developed for the mass production of both quarter micron large‐scale integrated memories and application specific integrated circuits (ASICs). To achieve a productive level of throughput, the system utilizes a cell‐projection method combined with variable shaped method and a continuously moving stage at variable speed depending on the pattern density. The system is operated at a 50 kV acceleration voltage and a 1 μC/cm2 dosage. Three stage deflectors have been developed to assure high‐speed deflection and highly accurate positioning. A fast pattern controller generates patern data at 200 ns shot‐cycle‐time with the positioning error correction and proximity effect correction. A high‐speed ceramic XY stage and an automatic wafer loder have been developed. The system is operated by a workstation which also provides data conversion. The estimated throughput of the system is 11 wafers/h for 0.3 μm ASICs and 20 wafers/h for quarter micron memories.

Dynamic micromagnetic field measurement by stroboscopic electron beam tomography

A stroboscopic electron beam tomography system for measuring the dynamic micromagnetic field of recording heads is presented. A pulsed electron beam, which is synchronized with the recording head driver, is scanned along the recording head surface from all directions. Integration of the magnetic field intensity along the beam path is calculated from the electron beam deflection angle. Intensity distributions of the dynamic magnetic field are calculated using a tomographic reconstruction algorithm. To obtain enough current even in pulsed electron beam operation, a high-brightness Ti/W thermal field emitter is used. This system was successfully applied in measuring the field distributions of a thin-film recording head, with 0.1 mu m spatial resolution and 1 ns time resolution at an operation frequency of 30 MHz. >

Alignment of CS2 in intense nanosecond laser fields probed by pulsed gas electron diffraction

A pulsed gas electron diffraction apparatus was developed and applied to investigate an alignment process of molecules in intense laser fields. A two-dimensional (2D) electron diffraction pattern of jet-cooled CS2 in intense nanosecond laser fields (1064 nm, ∼0.64 TW/cm2, 10 ns) was measured using short-pulsed 25 keV electron beam packets (∼7 ns) generated by irradiating a tantalum photocathode with the 4th harmonics of pulsed YAG laser light. The observed anisotropic 2D diffraction pattern was analyzed quantitatively by taking into account the spatio-temporal distributions of the laser pulses, the electron beam packets, and the molecular beam through a numerical simulation of the observed diffraction pattern. The anisotropy of the spatial distribution of molecular axes of CS2 in the laser polarization direction is accounted for by the effect of the intense laser fields. Considering the spatio-temporal averaging effect, the temporal pulse width of an electron packet required for real-time probing of the a...

Improved CD-SEM optics with retarding and boosting electric fields

Because of rapidly decreasing line-width of integrated circuits, it is necessary to measure and control their critical dimensions with high accuracy. Hitachi has developed a new critical-dimension-measurement scanning electron microscope S-9000 series, which has a new electron optics with retarding and boosting electric fields. The upper pole piece of the objective lens is kept at a high positive voltage with respect to the ground so as to reduce aberration of the objective lens drastically. To optimize the boosting voltage we have developed optics simulators that is capable of computing aberration coefficients in electric and magnetic mixed fields. At the optimized boosting voltage of around 5kV, 3nm resolution is achieved for a final accelerating voltage of 800V. The high boosting voltage is effective in imaging bottoms of contact holes having high aspect ratios.

Time resolved measurement of dynamic micro-magnetic field by stroboscopic electron beam tomography

Stroboscopic electron-beam tomography has been achieved for time-resolved measurement of the magnetic recording thin-film head. The transition characteristics of magnetic field distributions were compared; the driving current was found to have a temporal resolution of 1 ns. Both the driving current waveforms and the magnetic field distributions are measured by a pulsed electron beam with the same timing pulse gate. This measurement was successfully applied to Ni-Fe and CoTaZr amorphous thin-film disk heads. It was found that the magnetic field distribution change with time is not uniform and that the peak field is a few nanoseconds behind the driving current for Ni-Fe heads. The frequency characteristics of these heads correspond for the magnetic field delay to the driving current. The frequency characteristics of the head whose magnetic field delay is longer are inferior to those of the head whose magnetic field delay is shorter. >

Stroboscopic testing of LSIs with low voltage scanning electron microscope

A stroboscopic scanning‐ electron microscope (SEM) with 1 keV electrons has been developed to analyse the internal voltage waveforms in very large scale integrated circuits (VLSIs). A field emission gun and a short focal length objective lens are used to obtain a fine probe. Secondary electrons returning up through the objective lens are detected and analysed by a hemispherical retarding field energy analyser. The working distance of the objective lens is 3 mm, and a small stable probe of 0.1 μm in diameter with 1.6 nA in beam current is obtained. The linearity of the potential measurement is fairly good in spite of analysing secondary electrons which pass through the magnetic field. A minimum time resolution of 500 ps as well as a voltage resolution of 50 mV can be measured. This stroboscopic SEM has been successfully applied to evaluation of high speed waveforms in a ECL‐4K bit bipolar RAM.

Snorkel-type conical objective lens with E cross B field for detecting secondary electrons

A new optical system has been developed which employs a snorkel type conical objective lens that allows high resolution imaging at high tilt angles, up to 45 degrees. An E cross B field for detecting secondary electrons is utilized in this optical system in order to avoid influence upon the primary beam from the extraction field generated by the usual scintillator secondary electron detector. Spatial resolution of better than 4 nm at an accelerating voltage of 1 kV has been obtained from a secondary electron image, with a working distance of 3 mm.

Multi-sampling method in an EBT for logic waveform measurement

Abstract A multi-sampling method is applied to logic waveform measurement. In this method, a number of pulses are generated in one logic cycle; these pulses are synchronized with the device clock. It offers a rise-time resolution as high as that of the stroboscopic method and a measurement time shorter than that of the stroboscopic method by a factor equal to the number of pulses generated in the logic cycle. A developed SE detector with an 8ns response time is able to measure a logic waveform with a 50MHz clock rate and 100k clock cycles within a measurement time of 100 seconds which is 1/100,000 as that by a stroboscopic method.

High Spatial Resolution Spin-Polarized Scanning Electron Microscope

Spatial resolution of a spin-polarized scanning electron microscope has been improved to 0.2 µm for domain images of an iron sample. This value is comparable to that of the colloid-SEM (scanning electron microscope) method and is superior to that of other conventional reflection-type domain observation methods. This spin-polarized scanning electron microscopy is an excellent method for surface magnetic domain observation, due to not only high spatial resolution but also its other capabilities which conventional methods including the colloid-SEM method do not have.