Measurement of undercut etching by contact resonance atomic force microscopy.

We proposed a method for measuring undercut etching based on contact resonance atomic force microscopy (CR-AFM). Suspended undercut structures were fabricated through isotropic wet etching on a patterned SiN_x/Si architecture. The materials beneath the SiN_x masks with circular and rectangular shapes were partially etched to form center-supported thin plates. A clear contrast was observed between the supported and suspended regions by CR-AFM amplitude imaging, enabling accurate determination of the undercut boundary and the corresponding etched length. CR-spectroscopy measurements of the undercut dimensions were also applied by acquiring the contact stiffness distribution and by further fitting with models of analyzing the plate deflection. The etching rates given by both the imaging and spectroscopy measurements were in close accordance. The theoretical measurement error induced by finite CR-frequency to stiffness sensitivity was evaluated to be around 5% under our experimental settings. This work paves the way for in situ and real-time detection of undercut etching at the nanoscale and benefits relevant micro- and nano-fabrications. [ABSTRACT FROM AUTHOR]