Mr. Takuya Yamanaka Profile

Takuya Yamanaka

at Univ of Tokushima

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Proceedings Article | 3 June 2010 Paper

Modeling of charging effects in scanning ion microscopes

Kaoru Ohya, Takuya Yamanaka, Daiki Takami, Kensuke Inai

Proceedings Volume 7729, 77290V (2010) https://doi.org/10.1117/12.853488

KEYWORDS: Ions, Selenium, Silica, Gallium, Chemical species, Monte Carlo methods, Particles, Scanning electron microscopy, Microscopes, Ion beams

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Unwilling deformations of secondary electron (SE) images due to charging of an insulating layer on materials is one of important issues for semiconductor industry applications of scanning ion microscopes (SIM). This paper presents a Monte Carlo model of SE emission from SiO₂ in which the charging induced by ion bombardment at the energy range of tens of keV is taken into account. A self-consistent calculation is carried out for the transport of a projectile ion, recoiled material atoms and SEs, the creation of space charges trapped in the material and the resultant electric field in/out the material. Drift motion of trapped charges is calculated as well, where the recombination with a charge of opposite sign is taken into account. Therefore, the evolution of the charging is simulated with successive arrivals of ions. Since the surface voltage is positive due to ejection of SEs and injection of positive ions, some of ejected SEs are drawn back to the surface and can rebound on it; these SEs are unable to produce a net emission. Dynamic changes in the SE yield and surface voltage are compared among He ions, Ga ions and low-energy (<1 keV) electrons, along with the space charge distributions and the in/out electric fields. The net SE yield is decreased during ion bombardment and finally it vanishes, which is different from the case of electron bombardment where the net SE yield (including BSEs) is kept to one due to a balance between coming and outgoing electrons. Even if there is not net emission of SEs, the surface voltage does not reach any steady-state condition but progressively increases due to successive injection of positive ions. The growth rate of the surface voltage depends on both the SE yield with no charging and the spatial distribution of the ions penetrating into the material.

Proceedings Article | 24 March 2009 Paper

Simulation of secondary electron emission in helium ion microscope for overcut and undercut line-edge patterns

Takuya Yamanaka, Kensuke Inai, Kaoru Ohya, Tohru Ishitani

Proceedings Volume 7272, 72722L (2009) https://doi.org/10.1117/12.813889

KEYWORDS: Ions, Gallium, Selenium, Silicon, Ion beams, Electron beams, Monte Carlo methods, Scanning electron microscopy, Helium, Scanning helium ion microscopy

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In order to study the topographic contrast of line-edge patterns in a scanning ion microscope (SIM) using helium (He) beam, a Monte Carlo simulation of secondary electron (SE) emission from silicon (Si) by the impact of He ions in the energy range of tens of keV is performed. The edges with overcut and undercut profiles for different sidewall angles are modeled and the patterns are scanned by using 30 keV He ion beam, so that the line profiles of the SE intensity are calculated assuming zero-sized beams. The results are compared with those of 30 keV Ga ion and 1 keV electron beams. Furthermore, the pseudo-images of critical-dimension (CD) line patterns with different widths are constructed from the SE profiles. The calculated SE yields of Si for 10-40 keV He ions increase with increasing impact energy, which become larger than that for low-energy electrons (keV or less). When scanning the line edges formed on a Si surface, there appear both large and sharp peak and small dip of the SE yield. The height of the peak is much more for the He ion beam than the Ga ion and electron beams, whereas the width is less: the FWHMs are 3.8 nm for 30 keV Heion, 7.2 nm for 30 keV Ga-ion and 8.0 nm for 1 keV electrons. This indicates that the line edge is more clearly distinguished by He ions. The change in the sidewall angle causes the change in the shape of the hump in the SE profile at the sidewall of overcut edges due to the incident angle dependence of the SE yield, which is clearly seen for all beams. However, much less change in the line profiles of undercut edges is found for Ga ion and electron beams.

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