Pupil optimization of EUV low-n attenuated phase shift mask for improvement of random contact hole patterning proceedings

Extreme ultraviolet lithography (EUVL) is pivotal for advancing semiconductor manufacturing under 5nm technology nodes. This paper explores the integration of low-n attenuated phase shift masks (att-PSM) and advanced source mask optimization (SMO) technis to address the fundamental challenges posed by EUV lithography, particularly mask 3D (M3D) effects which degrade image quality due to phase errors induced by mask topography. We demonstrate that low-n PSMs significantly enhance optical contrast and reduce line edge roughness, making them crucial for achieving high-resolution patterns at ultra-fine pitches. Additionally, we employ sophisticated SMO strategies, including asymmetric illumination and customized wavefront engineering, to further refine the lithographic process and improvements in normalized image log-slope (NILS) and focus control are achieved. Through comprehensive simulations and experimental validations, we show that the strategic combination of these technologies not only mitigates the intrinsic limitations of EUV but also enhances the overall lithographic process. Through wafer evaluation, we optimized the illumination system for low-n attPSM, significantly contributing to improved best focus (BF) uniformity across different pattern pitches. We achieved a 15% improvement in local critical dimension uniformity (LCDU) compared to the binary (BIN) mask, reducing the LCDU from 2.6 nm to 2.21 nm. The results confirm that these integrated approaches significantly improve the printability of intricate patterns while maintaining high throughput and manufacturing yield, setting the stage for future advancements in EUV lithography technology.