Nanometer Scale Dimensional Metrology

Nanometer scale metrology for instrument calibration applications such as atomic force microscopy or scanning electron microscope calibrations will be focused on 100 μm by 100 μm range scale measurements using the NIST-developed calibrated atomic force microscope (C-AFM) will provide accurate height metrology for surface roughness and dimension metrology with picometer accuracy. The C-AFM will be used especially for the smaller length scales needed for AFM and SEM two-dimensional scale calibrations. The C-AFM is a custom-built instrument that has built-in metrology on all three axes of motion traceable to the SI (Systeme International d’Unites, or International System of Units) meter through the 633 nm wavelength of a He-Ne laser. The C-AFM also allows vertical scale calibrations, i.e., step height. The instrument, now in its fourth generation, will provide reference measurements for commercial standards suppliers and will be used to participate in international comparisons for nanometrology.

An atomic force microscope for traceable dimensional metrology has been developed by NIST for nanometer scale measurement applications. This instrument is called the calibrated AFM (C-AFM) and is a custom-built system that has integrated traceable displacement metrology on all three axes of motion. This is accomplished through the use of laser interferometers, and the 633 nm wavelength of a He-Ne laser is used to realize the SI meter. This instrument is now in its fourth generation and the current scanner has a lateral range of 100 μm and vertical range of up to 5 μm.

The C-AFM has been used on a Special Test basis to provide measurements to several external customers. These are typically commercial standards suppliers who use the results of our measurements as an internal reference to transfer traceability to their commercially available products. In this manner, NIST has been able to greatly extend our impact on the overall AFM user community.

This instrument has also been used to participate in three international measurements comparisons involving other national metrology institutes (NMI): (1) NANO4 – a comparison of one-dimensional sub-micrometer pitch measurements conducted in 1999; (2) NANO2 – a comparison of sub-micrometer step height measurements conducted in 2002; and (3) NANO5 – a comparison of sub-micrometer two-dimensional pitch measurements conducted in 2005. These comparisons were organized under the auspices of the BIPM. Participation is planned in a new comparison of one-dimensional pitch measurements that will be organized by the National Research Council Canada.

Additional goals for this program in the near to intermediate future are to measure a new set of internal step height masters for a commercial standards supplier. Also under consideration is the production of an SEM/SPM magnification standard reference material with 0.2 μm minimum pitch structures with sub-nanometer precision. This will be crucial for calibration of the scale and accurate operation of SEMs and SPMs for metrology applications.

• The C-AFM was used to perform a traceable 100 nm grating pitch measurement with 6 × 10^-4 relative expanded uncertainty in support of SEM metrology of gold nano particles for NIST Reference Material (RM) project.
• Completed NIST participation in an international round robin of two dimensional pitch measurements using the C-AFM. Two gratings – 1000 nm and 290 nm pitch – were measured.