Three-Dimensional Kelvin Probe Force Microscopy

Traditional Kelvin probe force microscopy (KPFM) is mainly limited to the characterization of two-dimensional (2D) surfaces, and in situ surface potential (SP) imaging along 3D device surfaces remains a challenge. This paper presents a multimode 3D-KPFM based on an orthogonal cantilever probe (OCP) that can achieve SP mapping of 3D micronano structures. It integrates three working modes: a bending mode for 2D horizontal surface imaging, a torsion mode for vertical sidewall imaging, and a vector tracking-based 3D scanning mode. The customized OCP has a nanoscale tip protruding from the side and underside of the cantilever, rather than the front, and the extended tip makes the proposed approach universally applicable for 3D detection from the nanometer to micrometer scale. The spatial resolution of the proposed method is analyzed by simulation, which shows it can reduce the cantilever homogenization effect. Linearity and energy resolution measurements show that the proposed method has comparable performance to traditional methods. A comparative experiment using a gold-silicon interface verifies the accuracy of the reported method in its bending and torsion modes. Further, the imaging ability of the 3D scanning mode is confirmed in the 3D characterization of a step grating. This technique is applied to the in situ characterization of a microforce sensor with microcomb structures. The experiment results show that this method can excellently achieve the 3D quantitative characterization of topography and SP, including critical dimensions and SP along a 3D device surface. This novel 3D-KPFM technique has many potential applications in the further exploration of 3D micronano devices.