Over the past few years, on product overlay (OPO) challenges have become serious yield limiters for the latest technology nodes, requiring new and innovative overlay (OVL) metrology solutions. OVL metrology systems must have excellent measurability capabilities to cover as many different layers as possible, minimize any systematic contribution to measured OVL and demonstrate low residuals and high correlation to AEI SEM and AEI in die overlay (IDO). OVL metrology system manufacturers are required to introduce new target designs, tool hardware (HW) and advanced algorithms to keep up with said challenges. The paper will present optical OVL solutions per segment: foundry, logic, DRAM, and 3D NAND. We will review various new technologies developed in the last year that improve the OVL measurement systems’ performance to meet the above challenges. We will see how the new innovative targets improve measurability and accuracy on imaging-based overlay (IBO) and scatterometry-based overlay (SCOL®). Then, we will review new hardware components designed to improve measurability and overall fleet matching. Lastly, we will discuss how advanced machine learning (ML), multi-wavelength (MWL) and signal-weighting algorithms improve measurability, accuracy, and overall measurement performance.
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