Self-calibration overlay on ribbon-FET SRAM-like targets using full Mueller broadband spectroscopic ellipsometry for advanced process control

High-Voltage (HV) SEM-based overlay has proven capable of providing accurate, after-etch inspection AEI overlay (OVL) for static calibration of traditional optical after-develop inspection (ADI) metrology. However, there are currently limited optical-based, device-like OVL metrologies at AEI that may enable higher spatial and temporal measurement densities. We present an approach using broadband spectroscopic ellipsometry on self-calibrated SRAM-like overlay targets located in the scribe line. Using ellipsometry signals from these targets, along with algorithms, we aim to decouple real overlay from non-overlay asymmetries, such as tilt, which are problematic for traditional optical techniques. Self-calibrated overlay on SRAM targets offers the following unique benefits over existing metrologies: (a) on-product overlay measurements that enable better non-zero overlay (NZO) offset control, (b) improved budget breakdown of NZO error sources, (c) the ability to decouple overlay and non-overlay asymmetries on the device for better edge placement error, and (d) the potential to measure multiple overlay align-pairs within one target. In this work, we show sensitivity and correlation to HV SEM on SRAM targets on four layers (blind wafers) and six align pairs, quantified by merits to assess solution robustness. We will discuss potential and preliminary results from simultaneous OVL and CD measurements on SRAM-like targets to provide edge placement error (EPE) feedback from a single measurement.