Atom-Based Standards and Fabrication

A primary goal of this project is to develop intrinsic calibration standards based on the crystalline lattice. The ultimate limit for nanoscale length metrology is the development of intrinsic calibration standards, where the reference dimensions are based on atom spacing within an ordered, crystalline lattice.  Using techniques developed within this project, advanced step height, linewidth and pitch standards exhibiting picometer accuracy are being developed, using an ultra-high vacuum scanning tunneling microscope (UHV-STM).  In addition, a project goal is to validate the use of atomic lattice spacing as a ruler through comparison with interferometric length measurements such as those performed in the Molecular Measuring Machine.  The atom-based dimensional metrology project is leveraging this knowledge to develop the metrology science needed to enable parallel, high-throughput, atomically-precise manufacturing for NIST standards development and for industrial applications.

The atom-based dimensional metrology project is developing a new, comprehensive approach to dimensional metrology using the atom spacings of a crystal as the fundamental “ruler” or scale.  Based on this metric, larger scale features will be etched into substrates to serve as critical dimension or pitch references for instruments having less-than-atomic resolution.  Crystal-lattice dimensional parameters will be validated through interferometer measurements.  This work will primarily be done by employing two complex multi chamber vacuum STMs.  The first system is a five chamber ultra high vacuum (UHV) facility regularly capable of producing 1 x 10-8 Pa base pressures, along with vibration isolation that yields a sub-100 pm noise floor.  The other system has a unique field-ion/field-electron microscope (FIFEM), which is used to image scanned probe tips on the atomic scale and is being used to develop repeatable, robust methods for atomically sharp STM tip production.  The project is developing improved nanofabrication methods using the STM to write atomic-scale features on hydrogen-terminated silicon substrates using scanning probe oxidation (a technique that was invented in PED in the 1990’s) for accurate nano-standard development.   Atom-based step height standards having picometer accuracy will also be developed, validated and characterized by an interferometer-instrumented atomic force microscope.
One fundamental goal for the project is to develop methods for repeatably producing atomically-sharp tungsten and alternative-material tips, and evaluate their atomic resolution imaging capabilities.  This includes a systematic evaluation of different crystalline materials capable of producing single atom tips or atomic structures defined for high resolution sub-nanometer imaging.  

This project has a substantial effort to develop atomically ordered silicon (100) surfaces for hydrogen termination.  Based on previous recent work in the project, these surfaces will be used to fabricate structures smaller than 5 nm in dimension for use in standards and nanotechnology research.  Since these samples are not available commercially, it is essential to develop both the metrology for atomic resolution measurements and the ability to fabricate and measure standards with atomic precision at the nanometer scale.  

A second research goal is the calibration of a prototype atom-based 1 nm step height standard with an accuracy of 10 pm.  This will include an industrial round robin comparison of atom-based 1 nm step height standards to validate the accuracy of the method and of the industry metrology base.