AVS 45th International Symposium
    Electronic Materials and Processing Division Thursday Sessions
       Session EM-ThP

Paper EM-ThP4
Side-Wall Damage in a Transmission Electron Microscopy Specimen of Crystalline Silicon Prepared by a Focused-Ion-Beam

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Electronic Materials and Processing Poster Session
Presenter: N. Kato, IBM, Japan
Authors: N. Kato, IBM, Japan
H. Saka, Nagoya University, Japan
Y. Kohno, IBM, Japan
Correspondent: Click to Email
Focused ion beam (FIB) milling has recently been widely used for the preparation of cross-sectional transmission electron microscopy (TEM) specimens. Inevitably, however, such specimens are caused a certain amount of damage by highly accelerated ion beams. The damage to the side-wall of a specimen is visible under TEM as amorphization, and the structure of the undamaged intermediate layer can be observed through the damaged layers. Nevertheless, these damaged layers do pose a serious problem for TEM observation, especially when high-resolution observation is required. Many techniques have been developed for reducing the damage, such as gas-assisted etching. In this study, we experimentally investigated the depth of the side-wall damage in silicon, and the effect of the damaged layer on TEM observation. The depth of damage caused by a 30-keV FIB without gas-assisted etching was 20 nm, which was reduced to 10 nm by lowering the acceleration voltage to 10 kV. Gas-assisted etching with iodine does not markedly reduce the damage, as would be expected from the enhanced etching ratio. We also investigated several methods for reducing the damage after FIB fabrication. Broad-argon-ion-beam milling reduced the damaged layer to 12 nm, and wet-etching the specimen with a mixture of nitric and hydrofluoric acid removed most of the damage. Removal of the amorphous silicon layer significantly improved TEM observation. No amorphous ring such as that observed in the diffraction pattern (DP) of the specimen immediately after FIB fabrication was seen in the DP of the wet-etched specimen, in which a silicon lattice fringe was clearly observed.