Application Example 2: Z-Contrast Sensitivity in Low-Voltage, High-Angle BSE Imaging

Abstract

Excellent Z-contrast sensitivity in high-angle BSE imaging is demonstrated through cross-sectional examination of an amorphous anodic alumina film, about 360nm thick, with fine impurity distributions. The distributions of impurities were determined by radio-frequency-powered glow discharge optical emission spectroscopy (rf-GDOES) depth profiling (Fig. E2.1b) and the film composition was determined by Rutherford backscattering spectroscopy (Fig. E2.2a). Briefly, the film consists of two major layers: an outer layer doped with B-species and the inner pure alumina layer next to the Al substrate. A waviness observed in the B-profile does not imply that boron distribution in the outer layer shows periodic variation. Such waviness is often seen in rf-GDOES profiles obtained from thin, transparent films deposited over mirror-polished substrates and is an artifact arising from an optical interference effect; in reality, B-species are distributed uniformly through the outer layer, as shown by the solid line [4]. The proportion of the outer layer to the total film thickness is 0.4. A narrow layer, about 10 nm, doped with W-species is present at a depth of 50 nm from the surface and is located in the outer layer doped with B-species. A clean and highly flat cross section of the anodic alumina film and the Al substrate, suitable for high-angle BSE imaging, was prepared by ultramicrotomy using a diamond knife following the procedures described in Application Example 7. The cross section was examined in the high-angle imaging mode; the accelerating voltage was 1.20 kV and the filtering grid bias voltage was 1.10kV.