Accuracy in Infrared Overlay Metrology

In 3D integration, particularly in wafer-to-wafer (W2W) hybrid bonding, achieving tight on-product overlay (OPO) control is increasingly critical as contact pitches are scaling down to 200 nm and beyond. To ensure reliable electrical connection, the total measurement uncertainty (TMU) of the associated overlay metrology must remain below 5 nm [1], [2]. Infrared overlay (IR OVL) metrology, which enables through-silicon measurements, faces unique challenges compared to traditional image-based overlay (IBO) techniques. This paper evaluates the TMU and trueness of state-of-the-art IR OVL tools and correlates their performance with IBO measurements conducted after removing the backside silicon of the bonded test vehicles, providing insight into the reliability of IR-based metrology in advanced bonding applications.