Accurate Quantification of Si/SiGe Interface Profiles via Atom Probe Tomography

Abstract

Pulsed laser atom probe tomography (APT) has enabled the investigation of semiconducting materials at sub‐nm length scales and 10 ppm chemical sensitivity. This has enabled APT to be the best technique for nanoscale detection of dopant distributions and low levels of chemical segregation at interfaces, which are both important for semiconductor processing; however, the accuracy of measured interfacial profiles is typically compromised by aberrations. Interfacial profiles in APT data will vary with respect to different interfacial combinations, especially when the evaporation field between two materials is drastically different. Here, the ability of APT to measure SiGe/Si/SiGe interfacial profiles is tested with an 8 nm Si well embedded in SiGe. The APT measurements are compared to those measured using scanning transmission electron microscopy (STEM) to evaluate reconstruction and post‐reconstruction processing methods to appropriately measure interfacial profiles using APT. Without post‐APT reconstruction processing, the measured Si/SiGe interfacial widths between APT and STEM match poorly, but after applying the z‐redistribution algorithm, the interfacial profiles are in good agreement. These results indicate that APT can be used to accurately identify SiGe/Si/SiGe interfacial profiles after application of the z‐redistribution algorithm, which will greatly impact the synergy between growth and characterization of semiconductor devices using Si/SiGe interfaces.

Atomic-Scale Insights into Semiconductor Heterostructures: From Experimental Three-Dimensional Analysis of the Interface to a Generalized Theory of Interfacial Roughness Scattering

“…Interestingly, we do not observe any systematic difference between the measured value of ℒ on the Ge→SiGe and SiGe→Ge interfaces. This observation differs from previous reports on both low- [18,31] and high-Ge content [30] Si/SiGe heterostructures. In fact, in these early reports larger widths were measured for the interface featuring a Ge content decreasing along the growth direction with respect to the opposite case, as one could expect considering the tendency to surface segregation of Ge atoms during the Si overlayer deposition.…”

“…Remarkably, the interface width here obtained is only slightly larger than that measured from low Ge content Si/SiGe multi-layers in Ref. [18], using the same technique. The value of ℒ we report here is also more than a factor ~2.5× smaller compared to those measured in Ge/Si0.2Ge0.8 multi-quantum well samples grown by reduced pressure CVD and plasma enhanced CVD reactors [29,30].…”

“…As already mentioned in the introduction, Valavanis et al [17] relaxed the hypothesis of interface abruptness with the scope of investigating SiGe multilayer systems, which typically feature non-negligible interface widths ℒ, in the 0.9-1.5 nm range [18,31]. Remarkably, the relevance of a proper modeling of diffuse interfaces has recently emerged also in the realm of III-V material systems [11,35].…”

“…Pulsed laser-assisted atom probe tomography (APT) has recently emerged as the ideal technique for evaluating the interface width ℒ [18]. Furthermore, APT makes it possible to reconstruct atom-by-atom the crystal structure in three dimensions and, potentially, to quantify other properties of buried interfaces, such as the rms roughness , the in-plane correlation length [19] ||, and the axial correlation length ⊥.…”

3D Atomic Mapping of Interfacial Roughness and Its Spatial Correlation Length in Sub-10 nm Superlattices

“…where c 0 is a vertical positioning parameter, x 0 is a horizontal positioning parameter, d 0 is a scaling parameter and the parameter ℒ determines the value of the interface width. [17] For the two interfaces shown in the inset of Figure 3 of sample S-6 is shown in Figure S6(a). The average Ge concentration within the Si 1−x Ge x layers of sample S-6 is ~24.4 at.% (±2.0%).…”