A CD probe with a tailored cantilever for 3D-AFM measurement

Abstract

A critical dimensional (CD) probe, such as a boot shaped probe, is widely used for measuring the sidewall profiles of nanostructures in atomic force microscopy (AFM). However, conventional CD probes usually have high spring constants that restrict their ability to operate in critical dimension scanning modes. Furthermore, the flexure spring constant of the tip is much smaller than the torsion spring constant of the cantilever, which probably makes the sidewall measurement unstable. Here, we proposed a method of tailoring the probe where the cantilever was trimmed to reduce the spring constant. The simulation results, using a finite element method (FEM), illustrated that both the flexure and torsion spring constants decreased nearly ten times. Meanwhile, the torsional resonant frequency decreased to below 1 MHz, which could benefit the torsional oscillation scanning. By using a focused ion beam (FIB), a CD probe with a rectangular cantilever was reprocessed. It was mounted to a home-built three-dimensional AFM system (3D-AFM), and had the flexure and torsion sensitivities precisely calibrated. The ratio of the flexure sensitivity to torsion sensitivity showed good accordance with the simulation results. Additionally, a grating standard sample was measured using the tailored probe under a modified step-in scanning mode, and the error due to torsional deformation of the tip was compensated. The measurement results demonstrated the validity of the tailored CD probe in 3D metrology.