Measurement of restricted duty cycle of 2D gratings based on diffraction efficiency

Morphology characterization techniques, such as atomic force microscopy (AFM) and scanning electron microscopy (SEM), are widely used by grating device manufacturers. However, AFM suffers from probe wear, limited imaging range, and slow scanning speeds, while SEM can cause surface damage due to electron beam effects, potentially compromising the detection of grating surface details. To address these issues, this study investigates the correlation between the duty cycle of a two-dimensional grating and the (0,0)-order reflection efficiency using rigorous coupled wave analysis (RCWA). The reflection efficiency curve of the (0,0)-order S-polarized probe light is taken as a function of the duty cycle, and a fast, non-destructive optical method for grating duty cycle detection is proposed. By selecting an appropriate incident angle and measuring the (0,0)-order reflection efficiency at S-polarization, the duty cycle of a restricted range of two-dimensional gratings can be determined, providing robust support for predicting the global surface morphology of gratings. This study introduces a novel method for non-contact grating surface topography detection that is simple, efficient, and low-cost. Combined with an ultra-high-precision displacement stage for scanning, this method enables large-area, non-destructive, and accurate grating duty cycle detection, offering significant advantages for practical grating manufacturing.