Atomic transport in three-dimensional nanostructures of silicon and germanium

(DFG, cooperation with WWU Münster, apl. Prof. Dr. Hartmut Bracht)

With increasing downscaling of semiconductor devices the surface-to-volume ratio increases. Accordingly, the properties of surfaces and interfaces will become increasingly important to control and engineer the electronic properties of nanoelectronic devices. Present experimental results on atomic transport in nanoobjects are very limited. In particular, self-diffusion, that is the most fundamental process of mass transport in condensed matter, was not yet studied in nanoscaled Si and Ge systems. In the framework of this project we will investigate size effects on self-diffusion in Si and Ge nanostructures to gain information on the properties of native point defects in these confined material systems. For this purpose isotopically modulated Si and Ge fin and pillar structures with different widths and diameters are prepared by means of nano imprint lithography (NIL) or electron beam lithography (EBL) followed by highly anisotropic reactive ion etching (RIE) preferentially performed at cryogenic temperatures. The isotope structures are ideal test structures for studying self-diffusion as function of the structure size, temperature, dopant concentration, ambient and irradiation conditions. The distribution of the labeled matrix and dopant atoms is measured with high resolution applying appropriate profiling techniques which involve atom probe tomography (APT), secondary ion mass spectrometry (SIMS), neutron reflectometry (NR), scanning spreading resistance microscopy (SSRM), scanning Kelvin probe microscopy (SKPM) and electrochemical capacitance voltage profiling (ECV). Scanning electron (SEM) and high resolution transmission electron microscopy (HRTEM) will be performed to analyze the morphology and structure of the Si and Ge nanoobjects before and after thermal treatments. The experimental results are compared to computer simulations to develop meaningful physical models of atomic transport in nanoscaled Si and Ge systems that consider the impact of electronic surface and interface states.

[Translate to English:] Regular arrangement of isotopically modulated Si nanopillars prepared by means of cryogenic RIE from a Si wafer with a top layer of (28Si(7nm)/30Si(13nm))20