Direct observation of the behavior of the heavy single atoms on amorphous carbon substrates

Using a scanning transmission electron microscope it is possible, by directly imaging single atoms, to investigate the motion and distribution of heavy (high-Z) atoms deposited on the surfaces of thin low-Z films. In this study, the heavy atoms U, Pt, Au, In, Cd, Ag, and Pd were deposited on 15-Å-thick amorphous carbon substrates. It is found that adatom motion is strongly dependent upon local substrate structure and adatom species. Diffusion coefficients and activation energies for single atoms, as well as dimers, trimers, etc., have been obtained by directly measuring the motion of the atoms. Pair-density and nearest-neighbor distributions were measured and used to derive the interatomic potential and the rate of adatom nucleation. It is found that the interatomic potential is very weak and long ranged

Computer simulations of submicron FIB system optics

The design of the optical elements for a focused ion beam (FIB) system having a 50 mm spot size over a 1 mm square field requires extensive computational analysis. We discuss the mathematical techniques applied to the components of interest in this submicron FIB system; the electrostatic lenses, the mass analyzer, and the electrostatic deflectors. The results of ion trajectory calculations predicted for the whole FIB column by the computer code snow are presented. The aberration coefficients to third order and a parametric study of a stigmatic Wien filter whose design includes entrance and exit fringe field effects will be considered. We also cover our optimization algorithms for selecting lens and deflector elements which demonstrate minimal chromatic and spherical aberrations and distortions. A spot symmetry and spot location map for the final 1 mm square field and its 50 nm image constraint is shown for mixed electronic configurations of dynamic focus, dynamic distortion, and dynamic stigmation correctors. A comparison of the computer predictions to measured values of lens parameters is given for a typical liquid metal source and its extractor lens. The equipotentials in the vicinity of a representative lens is plotted with emphasis on the dielectric‐conductor interface in order to demonstrate the significance of stressed electric fields to the hardware designer

Transverse thermal velocity broadening of focused beams from liquid metal ion sources

Experiments have shown that the target current density in focused ion beam columns have long ‘‘tails’’ outside the central submicron region. We show that these tails result from a transverse velocity distribution which has a Holtsmark probability density. Both theory and experiment show that the tails are reduced as the system magnification and source current are reduced

A focused ion beam secondary ion mass spectrometry system

This article describes a Ga+ focused ion beam secondary ion mass spectroscopy system, and measures several quantities of interest to aid in interpreting secondary ion mass spectroscopy results. We have measured sputter yields and rates, estimated the instrument efficiency, and calculated useful yields and practical sensitivities for a variety of elements used in the semiconductor industry. We have performed measurements at the system base pressure, and have also introduced oxygen and iodine to determine any enhancement effects

Fundamental limits to imaging resolution for focused ion beams

This article investigates the limitations on the formation of focused ion beam images from secondary electrons. We use the notion of the information content of an image to account for the effects of resolution, contrast, and signal‐to‐noise ratio and show that there is a competition between the rate at which small features are sputtered away by the primary beam and the rate of collection of secondary electrons. We find that for small features, sputtering is the limit to imaging resolution, and that for extended small features (e.g., layered structures), rearrangement, redeposition, and differential sputtering rates may limit the resolution in some cases

Observation of nonhexagonal superlattices in high-stage cesium intercalated graphite

Using a scanning transmission electron microscope with an electron beam size of ∼800 Å, we have found that unsaturated cesium intercalated graphite at 98±2 K exhibits multiple structural phases with a typical domain size of ∼1 μm. Electron diffraction patterns from individual structural islands were studied, and the p(2×2), p(3√×2), and p(3√×13−−√) in-plane superlattices were identified

High‐gain lateral pnp bipolar transistors made using focused ion beam implantation

We report the fabrication of lateral pnp bipolar transistors using focused ion beam (FIB) implants of boron and phosphorus for the collector and base, respectively. The implants of B+, P+, and P+ + were all at a dose of 1×1013 /cm2 and a beam voltage of 75 kV. These implants defined spaces between the emitter and collector regions of 0.5–1.50 μm; which, after diffusion and zero voltage depletion width effects were considered, produced effective on‐wafer device basewidths of ∼0.2 μm. For the best devices, values of hFE near 100 were obtained with good junction characteristics and at peak collector currents of 10 μA/μm of device width

Electron-Energy-Loss Study of Stage-1 Potassium-Intercalated Graphite

Electron-energy-loss spectra of stage-1 K-intercalated graphite single crystals were obtained with a scanning transmission electron microscope. The complex dielectric function with electric polarization perpendicular to the c axis was derived by Kramers-Kronig analysis. The energy-loss peak at 2.5 eV is consistent with previous optical measurements, while the splitting of the one at 27 eV can be interpreted by folding the Brillouin zone of pristine graphite. Splittings and shifts of the interband transitions were observed and compared with calculations

Fabrication of bipolar transistors by maskless ion implantation

The first focused ion beam (FIB) arsenic ion implants are reported. A shallow junction, vertical npn bipolar transistor fabricated by maskless implantation of B and As is described. For comparison, devices on the same wafer were also processed with conventional, broad‐beam B and/or As implants. Good transistor performance is obtained for each type of implanted transistor. Device characteristics for FIB and conventional implants are generally the same. However, initial results indicate that diode quality and junction leakage appear somewhat degraded (excess generation–recombination) for FIB arsenic implanted devices. Characteristics of FIB boron implanted devices obtained over an extended period have been measured. These data indicate that wafer‐to‐wafer dose uniformity and quality (diode ideality and leakage currents) is equal to that for conventional implants (standard deviation