Development of reference samples for nano-analysis (together with BAM) (Auflösungsvermögen), Calibration der dimensionellen Größen
Conception and development of nanostandards for the calibration of high-resolution microscopes (SPM, SEM)
Investigation into the interaction between probe and surface in scanning probe microscopes and their influence on the measurement (probing uncertainty)
Development of standards for dimensional nanometrology with scanning probe and scanning electron microscopes (diameter, pitch, tip geometry, etc.) and performance of investigations on them

As the lateral resolution of the measuring instruments is a central focal point for the analysis of nanoscale structures, the determination and regular control of the lateral resolution requires reference materials as adjusting aid. Rreference materials with regular structures in the range between the dimensions of the crystal lattice (d < 1 nm) and lithographic structures (d > 150 nm). have, however, so far not been available. The lateral resolution of most of the devices which analyse the surface with electron beams or ionic beams lies, however, exactly in this gap.
Within the scope of the project "Quality Assurance in Nanoanalysis", a new type of reference material was developed at the Bundesanstalt für Materialforschung und -prüfung (BAM). The reference material BAM-L002 "fringe patterns for length calibration and determination of the lateral resolution in the nanometer range" is the cross-grinding of a semiconductor layer system. The AlxGa1-xAs – InxGa1-xAS – GaAs layers were prepared with metal-organic gas phase epitaxy (Metal-Organic Chemical Vapour Deposition (MOCVD)) at the Institute for Solid-state Physics of the Berlin Technical University. The layer system on a GaAs substrate was embedded in conductive epoxy resin and then ground and polished. The surface processed in this way then shows fringes with widths between 0.4 and 500 nm.
The reference material allows the length scale to be calibrated and different device parameters such as lateral resolution, beam profile (half width and width of the increase from 16% to 84% on one step) and the smallest detectable structure to be determined or estimated. In addition, the fringe pattern contains a calibration path, lattices with different fringe widths, very small fringes as well as broad fringes with step transitions. The fringe widths and spacings are certified by measurements with a transmission scanning electron microscope (TEM). For this purpose, TEM bars were cut out with a focussed ionic beam (FIB) at different places of the semiconductor wafer and measured with a calibrated TEM.

Grafik:

Figure 1: The figure shows the fringe pattern with a Time of-Flight Secondary Ion Mass Spectrometer (TOF – SIMS)

The profile through the aluminium distribution shows that a lattice with 80 nm fringes is only just resolved. The indium distribution shows the clear evidence of an InAs fringe approx. 0.4 nm in width.