Tip-on-tip imaging and self-consistent calibration using critical dimension atomic force microscopy

Abstract

There are presently two major forms of atomic force microscopy (AFM) which are used for critical dimension (CD) metrology in semiconductor and nano-manufacturing metrology. One type, commonly referred to as CD-AFM, uses flared tips and two-dimensional surface sensing to enable scanning of features with near-vertical sidewalls. A major source of uncertainty in this type of CD-AFM metrology is the calibration uncertainty of the tip width (TW). Standards for traceable TW calibration have thus been developed both by national metrology institutes and by commercial suppliers. This paper describes work on a potential alternative approach using a self-consistency calibration of three CD-AFM tips. Due to the requirement for tip-on-tip imaging and challenges associated with this, the application of such methods in AFM metrology has been relatively limited. Initial results that are in agreement with the prior National Institute of Standards and Technology width calibration were obtained, and comparable levels of uncertainty should be achievable. Although the self-consistent approach is unlikely to supplant transmission electron microscope cross sections and the use of well-characterized standards, it may have value as a supporting method or for validation of a prior result, and it may ultimately be as useful for evaluation of tip shape parameters—such as vertical edge height—as for TW calibration.