A comparison of He and Ne FIB imaging of cracks in microindented silicon nitride

H Zhang,B.J Inkson,Y Zhou,M Mazaheri,A Baggott

doi:10.1016/j.matchar.2018.05.006

Abstract

Helium ion microscopy (HIM) offers potential as a high spatial resolution technique for imaging insulating samples that are susceptible to charging artifacts. In this study helium and neon ion microscopy are used to image cracking in microindented samples of the non-conductive ceramic silicon nitride. The crack morphology of radial cracks emanating from the microindentations has been characterized for two different compositions of silicon nitride, with and without conductive coatings. Gold coating enhances crack edge contrast, but masks grain contrast for both He and Ne ion-induced secondary electron (ISE) imaging. Carbon coating enables the crystalline and glassy phases to be distinguished, more clearly with Ne-ISE, and the cracking pathway is found to be primarily intergranular. Zones of <100 nm diameter depleted ion-induced secondary electron emission along the crack paths are identified, consistent with charging ‘hotspots’.

Highlights

Focused ion beam (FIB) microscopy has become a technique of choice for surface and near-surface microstructural characterization
It is found that the non-conductive silicon nitride can be directly imaged with He-induced secondary electrons (ISE) and an electron flood gun, with a low charging rate compared to SEM
Radial cracks and lateral cracks can be clearly identified by enhanced ISE yield at crack edges

Summary

Introduction

Focused ion beam (FIB) microscopy has become a technique of choice for surface and near-surface microstructural characterization. Conventional FIB microscopes use a liquid gallium ion source due to its stability at room temperature amongst other factors [1,2]. In the last decade, commercial FIB systems have become available that use gas-ion sources including neon and helium. The key advantage of a helium ion microscopy (HIM) FIB system is the potential for a smaller probe size (< 0.35 nm) than with electron and gallium beams. This enables higher spatial resolution depending on the imaging method chosen [3]. Images can be formed using either ion-induced secondary electrons (ISE) or secondary ions (ISI). ISIs tend to exhibit a lower generation ratio than that of ISEs. ISEs can be useful in imaging non-conductive samples as Ga+ implantation at the sample surface forms a conductive layer [4]

Methods

Results

Conclusion