High-precision CD extraction for silver-layered photoresists using Monte Carlo simulation

Accurate critical dimension (CD) measurement in metal-layered photoresist structures faces challenges due to the high atomic number of metallic materials. It enhances backscattered electron (BSE) yield, thereby increasing SE2 (secondary electrons generated by BSE) contributions. These SE2 electrons distort the edge profile and intensity distribution of the secondary electron (SE) signal in scanning electron microscopy (SEM). To address this, we propose a hybrid Monte Carlo simulation approach that separates primary (SE1) and backscatter-generated (SE2) secondary electron signals through physics-based models. By dynamically combining these components with optimized scaling, our method achieves high-fidelity fitting to experimental SE yields. The study verified the origin of SEM signal distortion in silver-layered structures, enabling precise CD extraction. Validation achieved sub-nanometer accuracy (correlation coefficient R > 0.98), with robustness against process variations. The work includes systematic investigations of accelerating voltage effects on the critical parameter k. Besides, a specialized CD extraction algorithm was developed for metal-layered substrates. This physics-based approach provides a reliable solution for metrology in advanced metal-integrated devices. Future work will extend the method to other high-Z materials and more accelerating voltages.