Atom probe tomography for the characterization of next generation (and beyond) CMOS devices

The ever-ongoing downscaling of semiconductor technology has led to a paradigm shift from planar to 3D devices. Industry has moved towards 3D architectures such as fin field-effect transistors, with next being nanosheets and nanowires on the roadmap for their better electrostatic control and reduced power dissipation [1]. Additionally, novel material systems are constantly being investigated to improve or even disrupt conventional CMOS technology with the introduction of entirely new concepts – think of 2D materials, systems portraying (topologically) protected states, or phases which exhibit exciting superconducting, spintronic, thermoelectric or ferroelectric properties, etc.

The performance of such nano-applications is tailored by the structure and chemical composition at the atomic level: a few displaced atoms can make the difference! Device fabrication and characterization has never been so challenging, as tomorrows nano-devices become increasingly complex, and new materials and ingenious fabrication processes that continue to unfold. Hence, a reliable 3D characterization technique with close to atomic resolution and high elemental sensitivity is not only a dream – it is a requirement!

Laser-assisted atom probe tomography (L-APT) has emerged as the promised solution. In a nutshell (Fig. a), L-APT is based on the concept of controlled field emission of atoms from a needle-shaped specimen by a time-resolved laser pulse with the mass (hence element) identification achieved through the ions’ time-of-flight. By collecting the ions on a 2D detector and tracking their arrival sequence, we can reconstruct the 3D volume of the analyzed sample with sub-nm resolution (Fig. b).

While L-APT offers promise, many challenges have yet to be solved. These challenges arise mainly from the underlying physics, where one must understand e.g., the short-pulsed laser interaction with a nanoscale tip, the field evaporation behavior of surface atoms in a heterogeneous system, atomic processes (diffusion) on the surface and during the ion’s flight sequence (molecular ion dissociation), etc. – all of which might intricately contribute to a faulty composition and/or element distribution being measured. Understanding these physical mechanisms and identifying their driving forces will bring us closer to a true, quantitative 3D nanoscale characterization method for future materials and devices.

In this project you will work with state-of-the-art APT equipment. You will have the possibility to explore a vast playground of experimental work, data reconstruction and analysis, and literature available in this field of research.

[1] W. Vandervorst et al., “Dopant, composition and carrier profiling of 3D structures”, Mater Sci Semicond Process 62, 31 (2017)
[2] A. Veloso et al., "Vertical Nanowire and Nanosheet FETs: Device Features, Novel Schemes ...." IEEE IEDM,11.1.1-11.1.4, (2019)