Physical Characterization

NaMLab engages in state-of-the-art material research for nanoscale applications in strong co-operation with its industry partners as well as with other laboratories to foster progress in industry oriented as well as basic research. The focus of physical characterization at NaMLab can be summarized as follows: The available high-resolution scanning electron microscope (HRSEM) is capable of providing high magnification images down to 2 nm resolution (Fig. 1). Besides top-view images, cross-sectional SEM imaging showing the entire layer architecture (in case of thin multilayer film structures) can be imaged easily by a switch of sample holders. Furthermore, the SEM is equipped with an EDX (energy dispersive) detector. A very accurate and trustworthy chemical composition determination of the samples is possible covering almost the entire periodic table. Another equally fascinating feature of HRSEM is the high resolution electron beam lithography (e-beam) for structuring e-beam resist with accuracy in the 15 nm regime.

Fig. 1:  SEM image of standing silicon fin fabricated on an SOI substrate with hardmask after RIE etching, “bird‘s view”.

The atomic force microscope (AFM) is equipped with the Nanoscope user interface for measurement and data analysis. Resolution in the order of 2 nm in the scanning direction and below 0.1 nm perpendicular to the scanning direction is routinely realized in mapping the surface topography. An example of an epitaxial grown GaN surface is shown in Fig. 2. The AFM can be operated in the conductive AFM (C-AFM) mode and in the mode of Scanning Spreading Resistance Microscopy (SSRM). C-AFM is used to investigate the local leakage current density of thin dielectric layers, SSRM is applied to map the spatial dopant distribution of two-dimensional cross-sectional structures in semiconductors. A special method for analyzing piezoelectric materials is the piezo force microscopy (PFM). In this method the vertical displacement of the AFM tip is measured in response to an electrical excitation of the sample. The PFM method is currently refined for the analysis of the ferroelectric switching behavior of thin films.

Fig. 2: Surface topography of MOCVD GaN with monolayer stepped terrace structure. Pits of shallow (deeper) depth indicate end points of threading edge (screw + mixed) dislocations.

X-ray diffraction (XRD): A multifunctional diffractometer allows high resolution X-ray diffraction, X ray diffraction in classical Bragg-Brentano set-up, grazing incidence diffraction and X-ray reflectivity as well as reciprocal space mapping and polefigure measurements in the same apparatus. The tool has a resolution of < 40 arcsec and is used for phase analysis, measuring reciprocal space maps,determining the composition of alloys, layer thickness and stress state. A high resolution X-ray diffraction measurement on an AlGaN/GaN superlattice structure is shown in Fig. 3.

Fig. 3: Measured and simulated high resolution X-ray diffraction pattern of AlGaN/GaN superlattices grown by molecular beam epitaxy at NaMLab.


Dr. Andre Wachowiak

Dr. Andre Wachowiak
Senior Scientist
Phone: +49 351 2124990-00