OPO improvements by moiré effect-based imaging

With the continuous shrinking of semiconductor device nodes, the reduction of on-product overlay (OPO) becomes extremely critical for high-yield IC (Integrated Circuit) manufacturing. This requires accurate overlay (OVL) process control which can be better achieved by using an optimized OVL target design and a more advanced metrology platform. The novel rAIM® imaging-based-overlay (IBO) target, which has a grating-over-grating structure with significantly smaller pitch sizes as compared to the standard advanced-imaging-metrology (AIM®) target, can improve OVL measurement accuracy by adopting a more device-compatible design with high Moiré sensitivity. This paper demonstrates the advantages of rAIM targets by comparing and quantifying their performance to standard AIM targets through key parameters including raw OVL, residuals, precision, and total measurement uncertainty (TMU). We also present the performance of rAIM targets on different OVL metrology platforms. We conclude that with an optimized target design and an advanced OVL measurement platform, rAIM targets can be an ideal overlay metrology solution for advanced dynamic random-access memory (DRAM) devices.