Accurate submicron edge detection using the phase change of a nano-scale shifting laser spot

Accurate edge detection with lateral super-resolution has been a critical issue in optical measurement because of the barrier imposed by the optical diffraction limit. In this study, a diffraction model that applies scalar diffraction theory of Fresnel-Kirchhoff is developed to simulate phase variance and distribution along edge location. Edge position is detected based on the phase variation that occurs on the edge with a surface step-height jump. To detect accurate edge positioning beyond the optical diffraction limit, a nanopositioning stage is used to scan the super steep edge of a single-edge and multi-edges submicron grating with nano-scale, and its phase distribution is captured. Model simulation is performed to confirm the phase-shifting phenomenon of the edge. A phase-shifting detection algorithm is developed to spatially detect the edge when a finite step scanning with a pitch of several tenth nanometers is used. A 180 nm deviation can occur during detection when the step height of the detecting edge varies, or the detecting laser spot covers more than one edge. Preliminary experimental results show that for the edge detection of the submicron line width of the grating, the standard deviation of the optical phase difference detection measurement is 38 nm. This technique provides a feasible means to achieve optical super-resolution on micro-grating measurement.