2:00 PM - 2:15 PM
▲ [7p-C13-2] Effect of surface condition on ion induced secondary electron contrast in carbon-based samples
Keywords:GFIS, Nitrogen, Secondary electron
The first decade after the commercial integration of a gas field ion source (GFIS) operating with light ions into a microscope has renewed the interest in the focused ion beam technology as the resolution is pushed into the sub-10-nm regime. Helium ions allow for unprecedented depth of view in the secondary electron (SE) imaging mode, and different contrast mechanisms from scanning electron microscopy give additional information about the imaged sample.
The GFIS is capable to generate tightly focused ion beams from other source gases as well, including hydrogen [1], neon [2] and nitrogen [3]. Regarding machining properties, the former ends up as implanted protons in the sample, which in turn avoids swelling that is affecting other gases. Neon and nitrogen, on the other hand, are significantly heavier and are a compromise between gallium ions with larger sputter yield and low resolution, and the hydrogen/helium beams with high resolution but low sputter yield. Nevertheless, nitrogen stands out among all the discussed ion species as it forms very strong covalent bonds. A recent study showed that the covalent bond is not broken during ionization, but instead upon sample impact [4]. The SE contrast was found to be affected by the imaging gas (helium or nitrogen), an effect especially prevalent in samples subjected to considerable oxygen reactive ion etching [5]. However, helium and nitrogen SE images were acquired in the same nanofabrication system, thus effects of the instrument on image formation are possible.
In our talk we will compare images acquired by helium in the Zeiss Orion Plus with those take by helium and nitrogen in the nanofabrication system. These images show that the nitrogen ion induced SE formation by nitrogen ions is especially sensitive to the surface properties of carbon. In some cases such difference can be significant (see Figure 1).
References:
[1] S. Matsubara et al., Microsc. Microanal., 22( S3), 2016. [2] R. H. Livengood et al., Nucl. Instrum. Methods Phys. Res. Sect. Accel. Spectrometers Detect. Assoc. Equip., 645(1), 2011. [3] F. Aramaki et al., in Proc. SPIE 8441, vol. 8441, p. 84410D–84410D–6, 2012. [4] M. E. Schmidt et al., J. Vac. Sci. Technol. B, 35(3), 2017. [5] M. E. Schmidt et al., Microsc. Microanal., 2017.
The GFIS is capable to generate tightly focused ion beams from other source gases as well, including hydrogen [1], neon [2] and nitrogen [3]. Regarding machining properties, the former ends up as implanted protons in the sample, which in turn avoids swelling that is affecting other gases. Neon and nitrogen, on the other hand, are significantly heavier and are a compromise between gallium ions with larger sputter yield and low resolution, and the hydrogen/helium beams with high resolution but low sputter yield. Nevertheless, nitrogen stands out among all the discussed ion species as it forms very strong covalent bonds. A recent study showed that the covalent bond is not broken during ionization, but instead upon sample impact [4]. The SE contrast was found to be affected by the imaging gas (helium or nitrogen), an effect especially prevalent in samples subjected to considerable oxygen reactive ion etching [5]. However, helium and nitrogen SE images were acquired in the same nanofabrication system, thus effects of the instrument on image formation are possible.
In our talk we will compare images acquired by helium in the Zeiss Orion Plus with those take by helium and nitrogen in the nanofabrication system. These images show that the nitrogen ion induced SE formation by nitrogen ions is especially sensitive to the surface properties of carbon. In some cases such difference can be significant (see Figure 1).
References:
[1] S. Matsubara et al., Microsc. Microanal., 22( S3), 2016. [2] R. H. Livengood et al., Nucl. Instrum. Methods Phys. Res. Sect. Accel. Spectrometers Detect. Assoc. Equip., 645(1), 2011. [3] F. Aramaki et al., in Proc. SPIE 8441, vol. 8441, p. 84410D–84410D–6, 2012. [4] M. E. Schmidt et al., J. Vac. Sci. Technol. B, 35(3), 2017. [5] M. E. Schmidt et al., Microsc. Microanal., 2017.