Dual-Probe Atomic Force Microscopy based on tuning fork probes for critical dimension metrology

Atomic force microscopy (AFM) is widely used for nano-dimensional metrology in semiconductor manufacturing and metrological system. However, the conventional AFM can't provide accurate CD characterization of nanostructures, due to its top-down configuration and probe-size effect. In this paper, we develop a dual-probe atomic force microscopy (DPAFM). Compared to conventional optical-lever based AFM, the DPAFM exploits two tuning fork probes that simplifies significantly the setup and can be controlled based on frequency-modulation (FM) mode. The developed DPFAM is implemented that builds a zero-reference point by dual-probe alignment firstly, following which, characterizes nanostructures from two sides independently with the two probes. The final CD feature is determined by matching profiles from the two probes based on the zero-reference point. The capability of the DPAFM is validated by experiments on a CD-standard structure, that achieves the true CD assessment with good accuracy and repeatability.