True 3D-AFM sensor for nanometrology

Abstract

A new three dimensional (3D) atomic force microscopic (AFM) probe, referred to as the 3D-Nanoprobe, is introduced. The 3D-Nanoprobe is realized by introducing flexure hinge structures to the cantilever of a conventional critical dimension AFM (CD-AFM) probe. It has quasi-isotropic stiffness in 3D directions and is thus more powerful for detecting 3D tip-sample interaction forces in AFM measurements. In addition, the stiffness of the 3D-Nanoprobe is balanced to the bending stiffness of slender CD-AFM tips, offering improved 3D sensitivity. In this paper, a design example of a 3D-Nanoprobe based on a CD-AFM probe with a tip nominal diameter of 70 nm is presented. The design parameters are optimized via analytic modelling and the finite element analysis (FEA) method. The simulation results indicate that the designed 3D-Nanoprobe has much better performance than that of the original CD-AFM probe, for instance, its stiffness’ anisotropy ratio (including the tip contribution) has been improved from 8:8:1 (x, y, z) to 0.9:0.9:1 (x, y, z). The probing sensitivity is improved by a factor of more than 106, 128 and 1.6 in x-, y- and z-direction, respectively. Moreover, the designed 3D-Nanoprobe has the first bending mode eigenfrequency of 84.4 kHz and the first torsional mode eigenfrequency of 346 kHz. The 3D-Nanoprobe has been manufactured by applying a focused ion beam (FIB) tool. Finally, to detect the full 3D interaction forces by the 3D-Nanoprobe, a new AFM-head prototype which consists of two independently adjustable dual optical levers have been developed.