Evaluation of carbon nanotube probes in critical dimension atomic force microscopes

Abstract

The decreasing size of semiconductor features and the increasing structural complexity of advanced devices have placed continuously greater demands on manufacturing metrology, arising both from the measurement challenges of smaller feature sizes and the growing requirement to characterize structures in more than just a single critical dimension. For scanning electron microscopy, this has resulted in increasing sophistication of imaging models. For critical dimension atomic force microscopes (CD-AFMs), this has resulted in the need for smaller and more complex tips. Carbon nanotube (CNT) tips have thus been the focus of much interest and effort by a number of researchers. However, there have been significant issues surrounding both the manufacture and use of CNT tips. Specifically, the growth or attachment of CNTs to AFM cantilevers has been a challenge to the fabrication of CNT tips, and the flexibility and resultant bending artifacts have presented challenges to using CNT tips. The Korea Research Institute for Standards and Science (KRISS) has invested considerable effort in the controlled fabrication of CNT tips and is collaborating with the National Institute of Standards and Technology on the application of CNT tips for CD-AFM. Progress by KRISS on the precise control of CNT orientation, length, and end modification, using manipulation and focused ion beam processes, has allowed us to implement ball-capped CNT tips and bent CNT tips for CD-AFM. Using two different generations of CD-AFM instruments, we have evaluated these tip types by imaging a line/space grating and a programmed line edge roughness specimen. We concluded that these CNTs are capable of scanning the profiles of these structures, including re-entrant sidewalls, but there remain important challenges to address. These challenges include tighter control of tip geometry and careful optimization of scan parameters and algorithms for using CNT tips.

An Overview of the Recent Progress in the Synthesis and Applications of Carbon Nanotubes

“…Under large compression forces, CNTs will bend without breaking, and when the applied force is removed, the CNT will recover its original conformation with little or no plastic deformation [228]. Due to the stiffness and wear resistance of CNTs, they are considered to be an ideal imaging tip for atomic force microscopy (AFM) applications [12,230].…”

“…The nanosized carbons (or nanocarbons) comprise fullerenes, graphene and CNT [2]. Extraordinary importance is given to graphene and CNTs, as they play a vital role in current advances based on nanomaterials, including conductive and high-strength composites [3], artificial implants [4], drug delivery systems [5], sensors [6], energy conversion and storage devices [7], radiation sources [8] and field emission displays [9], hydrogen storage media [10] and nanometer-sized semiconductor devices [11], probes [12], and interconnects [13]. Radushkevish and Lukyanovich first detected and described CNTs in 1952 [14], and later, the SWCNTs were observed by Oberin in 1976 [15].…”

True 3D Nanometrology: 3D-Probing with a Cantilever-Based Sensor

“…The commercial CD-tip cantilever has several limitations for 3D probing, such as a crosstalk in the yz - and zy -directions, a strong anisotropy ratio in compliance and small detectable signal for slender and compliant CD tips, as detailed in [ 10 ]. The 3D-Nanoprobe [ 10 ] was designed to overcome these limitations, which might lead to shaft probing [ 18 , 19 , 20 ], tip breakage [ 21 ], or measurement errors. It is based on a rectangular CD tip cantilever and is manufactured with focused ion beam (FIB).…”

Carbon nanomaterials and their application to electrochemical sensors: a review

“…• intrinsically small diameters [178] • high ratio aspects that allow them to probe deep crevices and trench structures scanning electron microscopy, which has improved the accuracy of CNT mounting compared to their previous digital control system [178].…”