Impact of even aberrations on alignment accuracy in image-processing-based systems

The alignment system is a critical sensor for ensuring the overlay performance of lithographic tools, with lens aberrations playing a significant role in determining alignment accuracy. This study investigates the influence of aberrations on alignment accuracy through both simulations and experiments. The findings reveal that even aberrations lead to variations in the sensitivity of odd aberration-induced misalignment. These variations are explained by analyzing the asymmetry of the optical system's impulse response function. Sensitivity curves were generated by numerical simulation using Hyperlith and validated through experimental measurements. The results refine the understanding of the impact of lens aberrations on alignment accuracy. The proposed sensitivity curve offers a foundation for optimizing error-correction models, ultimately improving alignment accuracy in lithographic processes.