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Thin Film Fracture Toughness and Focused Ion Beam (FIB) Milling

byZEISS Microscopy 5 May 2021 2 min read

Introduction

Researchers investigate possible ion damage during focused ion bean (FIB) structuring of metallic thin films.

Thin films and nanostructured materials are present in a growing number of daily-life appliances, tools and vehicles. While they provide massive gains in terms of performance and efficiency, they are also critical components that absolutely should not fail, lest a whole device would cease to function. Unfortunately, it is neither easy to measure nor to forecast their mechanical properties.

Dr. Benoit Merle is a group leader and faculty member with the University of Erlangen-Nuremberg in the Department of Materials Science and Engineering, Germany. His research focuses on gaining a fundamental understanding of the small-scale deformation of the materials (in the nanometer to micrometer range) in order to predict how thin films and nanostructured materials will deform and fail. His recent publication investigates focused ion beam (FIB) milling and fracture toughness characterization of gold thin films.

Previously, we had discovered why metallic thin films become increasingly brittle as their thickness is reduced. We used a nanomechanical technique requiring preliminary structuring the thin films samples with a focused ion beam (FIB). This inevitably introduces some ion damage to the specimens, which could introduce a bias in the measurements.

Our goal with this publication was to prove that the ion damage is too small to affect our nanoscale fracture toughness measurements.

Dr. Benoit Merle Group Leader and Faculty Member, University of Erlangen-Nuremberg, Germany

Geometry of notch milled in a gold film with FIB Ga ion species

Geometry of notch milled in a gold film with FIB Ga ion species
Geometry of notch milled in a gold film with FIB Ne ion species

Geometry of notch milled in a gold film with FIB Ne ion species
Geometry of notch milled in a gold film with FIB Xe ion species

Geometry of notch milled in a gold film with FIB Xe ion species

Assessing Possible Sample Damage from Different FIB Microscopes

In cooperation with Dr. Jeff Wheeler at ETH Zurich and with the Max-Planck Institute for the Science of Light, identical samples were processed with different FIB microscopes with the following ion technologies: gallium, neon and xenon. The Monte Carlo simulations and the literature predicted that the much different sizes of these ion species would result in much different damage to the specimens. This was confirmed by directly imaging the surrounding area of the structures by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) after FIB processing.

Read the full article here.

Varying the ion species did not noticeably affect our fracture toughness measurements on the gold thin films. We rationalized that the ion damage is so local and small compared to the size of the FIB-milled features that its effects are fortunately negligible and valid fracture toughness measurements can be carried out by nanomechanical testing.

Dr. Benoit Merle Group Leader and Faculty Member, University of Erlangen-Nuremberg, Germany