Standards for scanning probe microscopes
Processing facility for the efficient manufacturing of crystalline standards
PTB has been working on crystalline standards for dimensional calibration for several years. In these standards, the silicon crystal lattice serves as a kind of “natural ruler” to measure spacings of less than 100 nm with extreme accuracy. Crystalline standards can reach a much higher resolution (approx. 0.3 nm) with much smaller uncertainties (approx. 0.03 nm) than conventional standards, which yield results that are poorer by a factor of 10.
One advantage of crystalline standards is their inherent traceability: The spacing between the atoms in silicon is always the same, which spares us the task of measuring it tediously with special, metrologically traceable devices. These standards can thus be supplied at comparatively low cost, provided it is possible to produce large numbers of them simultaneously and reproducibly.
A new facility has been developed for this purpose at PTB. It enables a much better control of the fabrication process of such standards. After only a short running-in period, the facility was able to produce more and larger specimens in a single run than was previously possible. The yield (i.e., the number of functional chips produced) has more than doubled. At present, it is possible to simultaneously process four specimens per run. In its very first run, the facility was able to manufacture specimens with a crystalline surface and monoatomic steps. The second objective, the ability to better control the relevant processing conditions, has also been realized. It is therefore now possible to deal with fundamental issues such as the useful area and possible step heights.
This facility allows us to supply a sufficient number of new specimens for users and thus to have the standards disseminated from the metrology lab to routine industrial and laboratory applications. The next step will eventually consist in optimizing the manufacturing process with a view to improving process yield and output, automating the assessment of microscope measurements for users, and developing national and international standards to regulate their application.
Contact
Ingo Busch
Department 5.1
Surface Metrology
Phone: +49 531 592-6136
ingo.busch(at)ptb.de