We present atom probe analysis of 40nm wide SiGe fins embedded in SiO and discuss the root cause of artefacts observed in the reconstructed data. Additionally, we propose a simple data treatment routine, relying on complementary transmission electron microscopy analysis, to improve compositional analysis of the embedded SiGe fins. Using field evaporation simulations, we show that for high oxide to fin width ratios the difference in evaporation field thresholds between SiGe and SiO results in a non-hemispherical emitter shape with a negative curvature in the direction across, but not along the fin. This peculiar emitter shape leads to severe local variations in radius and hence in magnification across the emitter apex causing ion trajectory aberrations and crossings. As shown by our experiments and simulations, this translates into unrealistic variations in the detected atom densities and faulty dimensions in the reconstructed volume, with the width of the fin being up to six-fold compressed. Rectification of the faulty dimensions and density variations in the SiGe fin was demonstrated with our dedicated data treatment routine.
With scaling of semiconductor devices showing no signs of abating and three-dimensional structures now being developed, new metrologies to meet these demands are being sought. Atom probe tomography offers the potential to meet these challenges, and here, the authors present an in-depth study focused on finding useable conditions for accurate stoichiometric analysis of GaN and AlGaN. By varying the laser energy/power, changes in the average tip field were induced, and the resulting impact on the measured stoichiometry was investigated. A strong variation in the GaN stoichiometry as a function of the average tip field was found, although a range of conditions that enable accurate stoichiometry were determined. Moreover, the stoichiometric variation as a function of tip field was highly reproducible across instruments and laser wavelengths. However, for AlGaN, the N concentration was always underestimated. To try and establish the underlying cause of the N underestimation, potential loss mechanisms which include N2 sublimation, N2 neutral generation from molecular ion dissociation, and differences in the field of evaporation between the matrix elements and multihits were considered and are reported herein.
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