Tip on Tip Imaging and Self-Consistent Calibration for Critical Dimension Atomic Force Microscopy: Refinements and Extension to Second Lateral Axis.

One type of atomic force microscopy (AFM) used for critical dimension (CD) metrology is commonly referred to as critical dimension atomic force microscopy (CD-AFM); it uses flared tips and two-dimensional surface sensing to enable scanning of features with near-vertical sidewalls. An important consideration in this type of CD-AFM metrology is the calibration uncertainty of the tip width. Standards for traceable tip width calibration have thus been developed both by national metrology institutes (NMIs) and commercial suppliers. The National Institute of Standards and Technology (NIST) has previously reported the implementation of a self-consistency tip width calibration using three CD-AFM tips to image each other. The results of this method were shown to be consistent with prior calibrations based on transmission electron microscope cross-sections. In the present work, the extension of this method to tips smaller than 50 nm is demonstrated, as well as the extension of the method to include a second lateral axis.