Low temperature (200–600°C) annealing in the transmission electron microscope (TEM) is used to provide a significant noise reduction in phase images of focused-ion-beam-milled GaAs and Si p-n junctions recorded using off-axis electron holography, as well as increasing the measured phase shifts across the junctions. Our results suggest that annealing removes defects resulting from Ga+ implantation and reactivates dopant atoms in the thin TEM specimens. In GaAs, electrically inactive surface layer thicknesses are reduced from 80to17nm on each specimen surface after annealing at 500°C. In Si the improvement is from 25to5nm.

Off-axis and in-line electron holography have been used to determine the electrical properties of a silicon p-n junction. Specimens were prepared for transmission electron microscopy (TEM) by focused ion beam (FIB) thinning and examined in a biasing holder, with holograms recorded as a function of specimen thickness and applied reverse bias. The data revealed the important role played by the surfaces of the thin TEM sample which affect the electrostatic potential distribution within the specimen. The presence of electrically inactive layers, corresponding to the FIB-damaged amorphous surface and an additional crystalline layer, was inferred from the experimental results. Such effects must be taken into account if electron holography is to be used in a reproducible and quantitative way for the examination of semiconductor devices.

SummaryOff-axis electron holography in the transmission electron microscope (TEM) is used to measure two-dimensional electrostatic potentials in both unbiased and reverse biased silicon specimens that each contain a single p-n junction. All the specimens are prepared for examination in the TEM using focused ion beam (FIB) milling. The in situ electrical biasing experiments make use of a novel specimen geometry, which is based on a combination of cleaving and FIB milling. The design and construction of an electrical biasing holder are described, and the effects of TEM specimen preparation on the electrostatic potential in the specimen, as well as on fringing fields beyond the specimen surface, are assessed.

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