Nanometer scale elemental analysis in the helium ion microscope using time of flight spectrometry

TL;DR

This paper introduces a novel integration of time of flight spectrometry into helium ion microscopes, enabling high-resolution, lateral elemental analysis and depth profiling at the nanometer scale without compromising existing imaging capabilities.

Contribution

The work presents the first successful implementation of ToF-BS and ToF-SIMS in a helium ion microscope, achieving nanometer resolution and enabling direct elemental mapping and profiling.

Findings

Lateral resolution of ≤54 nm achieved

Time resolution of Δt ≤17 ns demonstrated

Compatible with standard SE imaging mode

Abstract

Time of flight backscattering spectrometry (ToF-BS) was successfully implemented in a helium ion microscope (HIM). Its integration introduces the ability to perform laterally resolved elemental analysis as well as elemental depth profiling on the nm scale. A lateral resolution of $\leq$ 54 nm and a time resolution of $\Delta t \leq$ 17 ns $(\Delta t/t \leq 5.4\%)$ are achieved. By using the energy of the backscattered particles for contrast generation, we introduce a new imaging method to the HIM allowing direct elemental mapping as well as local spectrometry. In addition laterally resolved time of flight secondary ion mass spectrometry (ToF-SIMS) can be performed with the same setup. Time of flight is implemented by pulsing the primary ion beam. This is achieved in a cost effective and minimal invasive way that does not influence the high resolution capabilities of the microscope when operating in standard secondary electron (SE) imaging mode. This technique can thus be easily adapted to existing devices. The particular implementation of ToF-BS and ToF-SIMS techniques are described, results are presented and advantages, difficulties and limitations of this new techniques are discussed.