Optimization toward non-zero offset stability in overlay control: trends and prospects

In this study, we explore the role of overlay non-zero offset stability (sNZO) control in advanced node semiconductor processes, specifically using the imec N14 metal layer process. Our focus is on optimizing signal, dual, and multi-wavelength (MWL) overlay measurements in scatterometry-based overlay (SCOL®) metrology to enhance robustness and accuracy. Innovative SCOL hardware developments enable broadband overlay measurements without throughput penalties, providing rich data for advanced algorithms. We examine the impact of recipe optimization on overlay stability, and the challenges of achieving precise overlay (OVL) metrology performance due to process-induced target asymmetry and design-rule variations. Error budget breakdowns for individual components are discussed, using emerging reference tools on targets and devices across various steps. Our findings highlight the potential of SCOL technologies to improve NZO control, emphasizing the prospects of achieving better stability in semiconductor processes.