CONTRAST FORMATION IN FOCUSED ION-BEAM IMAGES OF POLYCRYSTALLINE ALUMINUM

Focused ion beam secondary electron images of polycrystalline aluminum films are valuable in revealing the grain structure of the films with great clarity on a scale of < 50 nm. The contrast mechanism for focus ed ion beam images in crystalline materials was identified ten years a go as due to crystalline channeling of the ion beam. To our knowledge there has been no report which quantifies this mechanism either with r espect to the magnitude of the intensity changes or their angular depe ndence. The ''critical angles'' of the angular dependence are expected to depend on the source of the secondary electrons, which may be diff erent than the channeled angular dependence of backscattering or sputt ering, for example, because of the difference in the distance of appro ach between the ion and a target atom at which the physical mechanism of interest takes place. The experiment described here quantifies the change in intensity and angular width in the case of channeled 30 keV Ga ions in aluminum thin films. This has been accomplished through a n ovel combination of focused ion beam images and electron backscatter d iffraction measurements. Results of these experiments, and their possi ble implications for metallurgical imaging, will be discussed. (C) 199 5 American Vacuum Society.