Small pitch overlay imaging metrology targets for tight OPO control

Sub-2nm On Product Overlay (OPO), scribe line width reduction, and high-order scanner correctibles are driving innovative overlay (OVL) targets. One promising new imaging-based overlay (IBO) OVL target to address such challenging trends in multiple semiconductor segments is a small pitch AIM (sAIM). sAIM is in essence an IBO target with grating (previous layer) beside grating (current layer) which could be placed in a few layouts: square, rectangular, and Mosaic. In this work, we will present the sAIM operational concept and performance including Total Measurement Uncertainty (TMU), residuals, and accuracy (ADI on-target offset vs. ACI on-device or target), which is often referred to as Non-Zero Offset (NZO).