The three-dimensional architectures of novel semiconductor devices has triggered the development of material characterization techniques with three-dimensional atomic resolution capabilities. As explicitly recognized by the semiconductor industry, cfr the International Technology Roadmap for Semiconductors, atomprobe tomography (APT) is among the most promising ones to solve this need since it does provide 3D-atomic scale elemental mapping. However, whereas APT leads to the 3D-dopant distribution, its counterpart, the 3D-carrier distribution, attracks equal importance. For the latter purpose, we rely on Scanning probes concepts (SSRM, KPFM, C-AFM,...) whereby the tip of the SPM is exploited as a nm-scale electrical point contact.
The APT technique is based on the atom-by atom field evaporation of individual atoms from a needle-shaped sample by the combined effect of a high standing voltage and a pulsed laser. The use of time-of-flight mass spectrometry and projection (with 106 X magnification) on a 2D position-sensitive detector then enables APT to provide a full 3-dimensional, quantitative composition analysis of materials with an excellent sensitivity (~ 10 ppm,) and a near-atomic spatial resolution (δlateral ~ 2-3 Å, δdepth ~ 0.5 Å). This technology thus offers the unique possibility of unraveling the 3-dimensional structure of complex advanced materials at the atomic scale (see Si FinFET of Fig. 1).
Whereas APT has demonstrated staggering capabilities in relatively simple systems, achieving these also in heterogeneous systems which combine nanostructured materials (e.g. multilayers, embedded clusters or more complex 3D nanostructures) does require much more fundamental insight in the laser-object interaction (e.g. light absorption in a sub-wavelength object), evaporation physics and the impact of variable tip shapes on local magnification variations and data reconstruction artefacts, to understand effects such as non-uniform magnifications (lateral and in depth), blurring of interfaces, deviations in shape and size of nanostructures, apparent observations of clusters of a specific atomic species as induced by preferential retention or migration across the apex prior to field emission, deviations in the observed composition, etc.
Complementing the chemical with electrical (conductivity) information, requires extending the 2D-SPM modes towards novel concepts with 3D-localization and resolution. This can be achieved by Scalpel AFM which is a novel slice-and-view approach developed by imec, whereby the probe is alternatively removing material on the atomic scale and performing concurrent electrical measurements creating 3D-tomograms of conductivity. This new 3D metrology concept has attracted lots of attention from semiconductor manufacturers as well as from tool manufacturers
This PhD project aims at unraveling these fundamental phenomena of both concepts and explore ways to achieve a highly complementary metrology on individual devices whereby FIB lift-out is used to select individual devices. You will work with state of the art dual beam FIB and atomprobe and SPM systems and benefit from the integration in the characterization group of imec disposing of a multitude of characterization techniques in support of this project. It will also be done in very close collaboration with the process engineers of imec and its industrial partners. The end results will a methodology suited to contribute to the development of next generation technologies.
Three-dimensional analysis of a Si finFET (central core surrounded by Hf-oxide and Ti-metal gate) with atomprobe tomography. Every point is an actual atom (red=Si, green=Hf, light blue=Ti, dark blue=Ni). Reproduced from the paper by M. Gilbert et al., Ultramicroscopy 111, 530-534 (2011)
Physics (optics, solid-state, semiconductors), engineering.
Type of work:
60% experimental, 40% theoretical.
Supervisor: Wilfried Vandervorst
Daily advisor: Claudia Fleischmann and Kristof Paredis
When you apply for this PhD project, mention the following reference code in the imec application form: ref. STS 1704-19.