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Project

Atomic-scale redistribution during metallization of compound systems

In semiconductor devices, novel functionality and enhanced performance are achieved through reduced dimensionality and a rapidly expanding materials library, including compound and complex heterogeneous materials. Emerging semiconductor materials such as GeSn or GeSiSn hold the promise of enhanced device performance but are prone to (at present unknown) compositional changes (e.g. Sn precipitation or surface segregation) and structural changes (strain relaxation, defect formation) during heat treatments. Such treatments are required during metal contact formation (germanidation, silicidation...) whereby also elemental redistributions occur as a result of the concurring phase transformations. Faced with these evolutions, it becomes clear that grasping the complex interplay between the material properties (at nm-scale), the underlying physical/chemical principles and the electrical performance does require a 3D quantitative compositional and elemental analysis with a high sensitivity and atomic resolution. The need for this characterization can be fulfilled by novel metrology concepts such as atom probe tomography (APT) that combines 3D quantitative analysis with an excellent sensitivity (10 ppm) and a near-atomic spatial resolution (δlateral ~ 2-3 Å, δdepth ~ 0.5 Å). APT exploits the concept of field evaporation and ionization of atoms from the apex of a needle-shaped specimen (~ 100 nm tip radius) and their projection onto a position sensitive detector. Atom-by-atom evaporation is triggered by either voltage pulses (conducting specimens) or laser pulses superimposed on a standing voltage (conducting to poor or non-conducting specimens). In either case, mass identification of the emitted species is achieved by well-defined departure times, obtained by using ultra short voltage/laser pulses, in combination with the detection of the arrival time. Reverse- projection of the detected ions enables a tomographic reconstruction of the specimen, and hence full 3D quantitative analysis. Coupling APT analysis with electrical and structural characterization provides fundamental insight in nanoscale material interactions, modifications and their impact on electrical properties. Furthermore, the laser-assisted atom probe tomography (LAPT) has emerged as a very promising concept satisfying both requirements simultaneously combining the advantageous properties of SIMS or ERDA (mass spectrometry and isotope sensitivity) and those of TEM (spatial resolution).

Date:10 Oct 2017 →  28 Jan 2020
Keywords:atom probe tomography
Disciplines:Nuclear physics, Condensed matter physics and nanophysics, Instructional sciences, Applied mathematics in specific fields, Elementary particle and high energy physics, Quantum physics, Classical physics, Other physical sciences
Project type:PhD project