We have investigated the bonding nature and hole-electron Coulomb interaction U in thin C 60 films on Be(0001) surfaces using valence-band and corelevel photoemission, inverse photoemission, and near-edge x-ray absorption spectroscopies. The C 60 monolayer had strong covalent bonding with the Be substrate, producing a nearly insulating film, in contrast to a metallic overlayer due to charge transfer observed on many other metallic surfaces. The effect of polarization of surrounding molecules and the image potential decreases the energy gap and U , but the bonding-antibonding contribution increases the gap at the interface. The measured U in thin solid films agrees well with a model calculation using gas-phase values. The deduced hole-electron attraction on the surface is about 0.7 eV larger than the reported hole-hole repulsion determined by Auger spectroscopy. On the basis of the surface-solid difference, the newly estimated value of U for hole-hole correlation places doped C 60 compounds nearer the metallic side of a Mott transition.

Improved resolution of an available i-line (365 nm) stepper using a phase-shifting mask is discussed. The resolution investigated here is not only for periodic lines but also for isolated spaces and hole patterns. To reduce the sizes of isolated space images for printing fine single spaces on a wafer, two additional line apertures with widths smaller than the critical dimension of the stepper lens are placed on each side of the main aperture of the mask. The optical phase of light passing through the main aperture and those through additional apertures are opposite. The additional apertures play a role in reducing the bright feature size to less than the line spread function of the lens. Similarly, printing a fine hole is accomplished by using a main aperture surrounded by four additional apertures. The intensity distribution on the wafer surface is simulated by comparing the images obtained with a phase-shifting mask and those obtained with a conventional transmission mask. Printing fine patterns are performed using an i-line stepper with a numerical aperture (NA) of 0.42. A pattern of 0.3 μm lines and spaces, 0.3 μm isolated spaces, and 0.4 μm hole patterns are resolved using the phase-shifting mask. The process latitudes and the effects of variations in the optical phase of the additional apertures are also investigated. The image simulations and experimental results suggest that the phase-shifting mask improve not only resolution but also exposure latitude and focus latitude. Furthermore, it is found that it is possible to control the position of the best focal plane by changing the optical phases of the additional apertures.

Cold-field-emission current from a tungsten ⟨310⟩ emitter in a scanning electron microscope (SEM) gun, evacuated by an ion pump and a supplementary nonevaporative getter pump, was stabilized. It was verified that the probe current from a local (310) crystal plane exhibits different time variations in comparison to that of total current. As for the probe current under a pressure of 2×10−9 Pa, a stable plateau region—which lasted about 4 h—appeared just after flashing of the emitter. By observing emission patterns, it was verified that these different emission characteristics are originated from the anisotropy of current decay in accordance with crystal planes. With low-temperature “mild flashings” at 700 °C, the plateau region was extended to 12 h, which is long enough for practical SEM application. The superior properties of the plateau region, namely, high current, low noise, and small current variation, will enhance the performance and usability of electron microscopes.

Observation at low voltage using scanning electron microscopes (SEMs) enables the characterization of surface details on specimens on a nanometer scale and is widely used in science and industry. However, the energy width of the electron source restricts the spatial resolution of SEMs at low voltage, but it can be narrowed by lowering the work function of the emitter material. Here, we developed a cold field emitter using a cerium hexaboride single crystal (CeB6-CFE) as a monochromatic electron source. The work function of the CeB6 (310) plane was estimated to be as low as 2.25 ± 0.17 eV, and the energy width ranged from 0.17 to 0.26 eV for angular current densities ranging from 0.10 to 80 μA/sr. This energy width was 20% to 30% narrower than that of conventional W(310)-CFEs. Using the CeB6-CFE, the spatial resolution of the SEM at an acceleration voltage of 0.5 kV was improved by 11% compared with that of an SEM using the W(310)-CFE.

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